How many distinct ways are there to traverse the edges of an N-dimensional hypercube?
I have an N-dimensional hypercube, and would like to traverse the edges so that I reach each vertex exactly once. One path that satisfies this property is known as the Gray code, but there are many others. How many such paths are there? Paths that can be mapped to each other by the symmetries of the hypercube may or may not be counted as distinct, depending on your preference.
combinatorics graph-theory
add a comment |
I have an N-dimensional hypercube, and would like to traverse the edges so that I reach each vertex exactly once. One path that satisfies this property is known as the Gray code, but there are many others. How many such paths are there? Paths that can be mapped to each other by the symmetries of the hypercube may or may not be counted as distinct, depending on your preference.
combinatorics graph-theory
2
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
1
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31
add a comment |
I have an N-dimensional hypercube, and would like to traverse the edges so that I reach each vertex exactly once. One path that satisfies this property is known as the Gray code, but there are many others. How many such paths are there? Paths that can be mapped to each other by the symmetries of the hypercube may or may not be counted as distinct, depending on your preference.
combinatorics graph-theory
I have an N-dimensional hypercube, and would like to traverse the edges so that I reach each vertex exactly once. One path that satisfies this property is known as the Gray code, but there are many others. How many such paths are there? Paths that can be mapped to each other by the symmetries of the hypercube may or may not be counted as distinct, depending on your preference.
combinatorics graph-theory
combinatorics graph-theory
asked Nov 29 '18 at 14:49
Display NameDisplay Name
2008
2008
2
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
1
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31
add a comment |
2
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
1
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31
2
2
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
1
1
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31
add a comment |
1 Answer
1
active
oldest
votes
This really is a sketch of a lower bound--but is too long for the comments
The lower bound for the number $X_n$ of Hamiltonian cycles in $H_n$ is at least something like $2^{2^n}$. In fact, $X_{n+1} geq 2^{2^n}X_n$.
Indeed, let $Q = v^0v^1ldots v^{2^n}$ be a Hamiltonian cycle in $H_{n}$. We will construct $2^{2^{n}}$ Hamilonian cycles in $H_{n+1}$ from $Q$.
Let $w^0w^1 ldots w^{2^n}$ be vertices such that (a) the first $n$ bits of $w^i$ are the same as the first $n$ bits of $v^i$, but the $n+1$-th bit of $w^i$ is free (for $i=0,1,2, ldots, 2^n-1$). So $2^{2^n}$ ways to chose the $w^i$s.
Let $H^i_2$ be the 4-vertex Hamiltonian path in the 4-vertex hypercube ${v^i,v^{i+1},v^i+ {bf{e}}_{n+1}, v^{i+1}+{bf{e}}_{n+1} }$ starting from $w^i$ and ending at $w^{i+1}$, where ${bf{e}}_l$ is the element where the $l$-th coordinate is 1 and the rest are all 0. [Note that $w^i in {v^i,v^i+ {bf{e}}_{n+1}}$, and $w^{i+1} in {v^{i+1},v^{i+1}+ {bf{e}}_{n+1}}$]
Then let $Q$ be the Hamiltonian cycle consisting of the $H^i_2$s concatonated. This specifies $2^{2^n}$ distinct Hamiltoninan cycles in $H_{n+1}$ from one Hamiltonian cycle $Q$ in $H_n$. In fact, if $X_n$ is the number of Hamiltoninan cycles in $H_n$ then $X_{n+1} geq 2^{2^n} X_n$.
The (trivial) upper bound $U_n$ for the number of Hamiltonian cycles in $H_n$ is $n^{2^n} = 2^{2^n log n}$ (given the $i$-th vertex of the Hamiltonian cycle there are only at most $n$ choices for the $(i+1)$-th vertex), so letting $L_n$ be the lower bound derived above, we note that $log log U_n le log log L_n + log log n$.
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3018718%2fhow-many-distinct-ways-are-there-to-traverse-the-edges-of-an-n-dimensional-hyper%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
This really is a sketch of a lower bound--but is too long for the comments
The lower bound for the number $X_n$ of Hamiltonian cycles in $H_n$ is at least something like $2^{2^n}$. In fact, $X_{n+1} geq 2^{2^n}X_n$.
Indeed, let $Q = v^0v^1ldots v^{2^n}$ be a Hamiltonian cycle in $H_{n}$. We will construct $2^{2^{n}}$ Hamilonian cycles in $H_{n+1}$ from $Q$.
Let $w^0w^1 ldots w^{2^n}$ be vertices such that (a) the first $n$ bits of $w^i$ are the same as the first $n$ bits of $v^i$, but the $n+1$-th bit of $w^i$ is free (for $i=0,1,2, ldots, 2^n-1$). So $2^{2^n}$ ways to chose the $w^i$s.
Let $H^i_2$ be the 4-vertex Hamiltonian path in the 4-vertex hypercube ${v^i,v^{i+1},v^i+ {bf{e}}_{n+1}, v^{i+1}+{bf{e}}_{n+1} }$ starting from $w^i$ and ending at $w^{i+1}$, where ${bf{e}}_l$ is the element where the $l$-th coordinate is 1 and the rest are all 0. [Note that $w^i in {v^i,v^i+ {bf{e}}_{n+1}}$, and $w^{i+1} in {v^{i+1},v^{i+1}+ {bf{e}}_{n+1}}$]
Then let $Q$ be the Hamiltonian cycle consisting of the $H^i_2$s concatonated. This specifies $2^{2^n}$ distinct Hamiltoninan cycles in $H_{n+1}$ from one Hamiltonian cycle $Q$ in $H_n$. In fact, if $X_n$ is the number of Hamiltoninan cycles in $H_n$ then $X_{n+1} geq 2^{2^n} X_n$.
The (trivial) upper bound $U_n$ for the number of Hamiltonian cycles in $H_n$ is $n^{2^n} = 2^{2^n log n}$ (given the $i$-th vertex of the Hamiltonian cycle there are only at most $n$ choices for the $(i+1)$-th vertex), so letting $L_n$ be the lower bound derived above, we note that $log log U_n le log log L_n + log log n$.
add a comment |
This really is a sketch of a lower bound--but is too long for the comments
The lower bound for the number $X_n$ of Hamiltonian cycles in $H_n$ is at least something like $2^{2^n}$. In fact, $X_{n+1} geq 2^{2^n}X_n$.
Indeed, let $Q = v^0v^1ldots v^{2^n}$ be a Hamiltonian cycle in $H_{n}$. We will construct $2^{2^{n}}$ Hamilonian cycles in $H_{n+1}$ from $Q$.
Let $w^0w^1 ldots w^{2^n}$ be vertices such that (a) the first $n$ bits of $w^i$ are the same as the first $n$ bits of $v^i$, but the $n+1$-th bit of $w^i$ is free (for $i=0,1,2, ldots, 2^n-1$). So $2^{2^n}$ ways to chose the $w^i$s.
Let $H^i_2$ be the 4-vertex Hamiltonian path in the 4-vertex hypercube ${v^i,v^{i+1},v^i+ {bf{e}}_{n+1}, v^{i+1}+{bf{e}}_{n+1} }$ starting from $w^i$ and ending at $w^{i+1}$, where ${bf{e}}_l$ is the element where the $l$-th coordinate is 1 and the rest are all 0. [Note that $w^i in {v^i,v^i+ {bf{e}}_{n+1}}$, and $w^{i+1} in {v^{i+1},v^{i+1}+ {bf{e}}_{n+1}}$]
Then let $Q$ be the Hamiltonian cycle consisting of the $H^i_2$s concatonated. This specifies $2^{2^n}$ distinct Hamiltoninan cycles in $H_{n+1}$ from one Hamiltonian cycle $Q$ in $H_n$. In fact, if $X_n$ is the number of Hamiltoninan cycles in $H_n$ then $X_{n+1} geq 2^{2^n} X_n$.
The (trivial) upper bound $U_n$ for the number of Hamiltonian cycles in $H_n$ is $n^{2^n} = 2^{2^n log n}$ (given the $i$-th vertex of the Hamiltonian cycle there are only at most $n$ choices for the $(i+1)$-th vertex), so letting $L_n$ be the lower bound derived above, we note that $log log U_n le log log L_n + log log n$.
add a comment |
This really is a sketch of a lower bound--but is too long for the comments
The lower bound for the number $X_n$ of Hamiltonian cycles in $H_n$ is at least something like $2^{2^n}$. In fact, $X_{n+1} geq 2^{2^n}X_n$.
Indeed, let $Q = v^0v^1ldots v^{2^n}$ be a Hamiltonian cycle in $H_{n}$. We will construct $2^{2^{n}}$ Hamilonian cycles in $H_{n+1}$ from $Q$.
Let $w^0w^1 ldots w^{2^n}$ be vertices such that (a) the first $n$ bits of $w^i$ are the same as the first $n$ bits of $v^i$, but the $n+1$-th bit of $w^i$ is free (for $i=0,1,2, ldots, 2^n-1$). So $2^{2^n}$ ways to chose the $w^i$s.
Let $H^i_2$ be the 4-vertex Hamiltonian path in the 4-vertex hypercube ${v^i,v^{i+1},v^i+ {bf{e}}_{n+1}, v^{i+1}+{bf{e}}_{n+1} }$ starting from $w^i$ and ending at $w^{i+1}$, where ${bf{e}}_l$ is the element where the $l$-th coordinate is 1 and the rest are all 0. [Note that $w^i in {v^i,v^i+ {bf{e}}_{n+1}}$, and $w^{i+1} in {v^{i+1},v^{i+1}+ {bf{e}}_{n+1}}$]
Then let $Q$ be the Hamiltonian cycle consisting of the $H^i_2$s concatonated. This specifies $2^{2^n}$ distinct Hamiltoninan cycles in $H_{n+1}$ from one Hamiltonian cycle $Q$ in $H_n$. In fact, if $X_n$ is the number of Hamiltoninan cycles in $H_n$ then $X_{n+1} geq 2^{2^n} X_n$.
The (trivial) upper bound $U_n$ for the number of Hamiltonian cycles in $H_n$ is $n^{2^n} = 2^{2^n log n}$ (given the $i$-th vertex of the Hamiltonian cycle there are only at most $n$ choices for the $(i+1)$-th vertex), so letting $L_n$ be the lower bound derived above, we note that $log log U_n le log log L_n + log log n$.
This really is a sketch of a lower bound--but is too long for the comments
The lower bound for the number $X_n$ of Hamiltonian cycles in $H_n$ is at least something like $2^{2^n}$. In fact, $X_{n+1} geq 2^{2^n}X_n$.
Indeed, let $Q = v^0v^1ldots v^{2^n}$ be a Hamiltonian cycle in $H_{n}$. We will construct $2^{2^{n}}$ Hamilonian cycles in $H_{n+1}$ from $Q$.
Let $w^0w^1 ldots w^{2^n}$ be vertices such that (a) the first $n$ bits of $w^i$ are the same as the first $n$ bits of $v^i$, but the $n+1$-th bit of $w^i$ is free (for $i=0,1,2, ldots, 2^n-1$). So $2^{2^n}$ ways to chose the $w^i$s.
Let $H^i_2$ be the 4-vertex Hamiltonian path in the 4-vertex hypercube ${v^i,v^{i+1},v^i+ {bf{e}}_{n+1}, v^{i+1}+{bf{e}}_{n+1} }$ starting from $w^i$ and ending at $w^{i+1}$, where ${bf{e}}_l$ is the element where the $l$-th coordinate is 1 and the rest are all 0. [Note that $w^i in {v^i,v^i+ {bf{e}}_{n+1}}$, and $w^{i+1} in {v^{i+1},v^{i+1}+ {bf{e}}_{n+1}}$]
Then let $Q$ be the Hamiltonian cycle consisting of the $H^i_2$s concatonated. This specifies $2^{2^n}$ distinct Hamiltoninan cycles in $H_{n+1}$ from one Hamiltonian cycle $Q$ in $H_n$. In fact, if $X_n$ is the number of Hamiltoninan cycles in $H_n$ then $X_{n+1} geq 2^{2^n} X_n$.
The (trivial) upper bound $U_n$ for the number of Hamiltonian cycles in $H_n$ is $n^{2^n} = 2^{2^n log n}$ (given the $i$-th vertex of the Hamiltonian cycle there are only at most $n$ choices for the $(i+1)$-th vertex), so letting $L_n$ be the lower bound derived above, we note that $log log U_n le log log L_n + log log n$.
edited Nov 29 '18 at 19:48
answered Nov 29 '18 at 16:50
MikeMike
3,148311
3,148311
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3018718%2fhow-many-distinct-ways-are-there-to-traverse-the-edges-of-an-n-dimensional-hyper%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
The name for what you're asking about is "Hamiltonian path." The short answer to your question is "a lot." According to this paper (ftp.inf.ethz.ch/doc/tech-reports/6xx/601.pdf), the number of Hamiltonian cycles on the $n$-dimensional hypercube $Q_n$ grows superexponentially; there are $6$ cycles (all automorphic) for $n = 3$, but for $n = 7$, the best known upper bound is about $2.5 times 10^{67}$. Note that every Hamiltonian cycle on $Q_n$ yields $2^n$ distinct paths by removing one edge of the cycle, and there are paths that can't be completed into cycles.
– Connor Harris
Nov 29 '18 at 15:14
You could try a more-or-less brute-force computer search, but I don't think this would be tractable beyond $n = 5$.
– Connor Harris
Nov 29 '18 at 15:15
@ConnorHarris If only an upper bound is known, feel free to post that as an answer and I will accept it. Unless of course someone decides to announce their new result here. ;)
– Display Name
Nov 29 '18 at 15:42
Well, $n!$ is an immediate lower bound; let $Q=u^0u^1ldots u^{2^n}$ be a Hamiltonian path on $H_n$ and let $pi$ be any permutation in $S_n$. Then let $pi(Q) = u^0v^1 ldots v^{2^n}$ be the Hamiltonian path specified as follows: let $k$ be such that $u^j$ and $u^{j+1}$ differ precisely in the $k$-th bit. Then $v^j$ and $v^{j+1}$ differ precisely in the $pi(k)$-th bit.
– Mike
Nov 29 '18 at 16:10
1
See OEIS sequences A003043 and A091299.
– Robert Israel
Nov 29 '18 at 18:31