This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A308155 #15 Feb 16 2025 08:33:55
%S A308155 1,11,1761,6560212131,282779810128722710004851715561,
%T A308155 22612323802416302740572466532825193607455652273991093701620185148186749274755003474250171
%N A308155 Number of (undirected) cycles in the n-Hanoi graph.
%C A308155 a(7) has 266 decimal digits and a(8) has 796 decimal digits. - _Andrew Howroyd_, Sep 10 2019
%C A308155 Also the number of chordless cycles in the (n+1)-Hanoi graph. - _Eric W. Weisstein_, May 23 2023
%H A308155 Andrew Howroyd, <a href="/A308155/b308155.txt">Table of n, a(n) for n = 1..8</a>
%H A308155 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/ChordlessCycle.html">Chordless Cycle</a>
%H A308155 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GraphCycle.html">Graph Cycle</a>
%H A308155 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/HanoiGraph.html">Hanoi Graph</a>
%F A308155 a(n) = Sum_{k=1..n} 3^(n-k)*A125295(k-1)^3. - _Andrew Howroyd_, Sep 10 2019
%t A308155 a[0] = 1; a[n_] := a[n] = a[n - 1]^2 (a[n - 1] + 1); Table[Sum[3^(n - k) a[k - 1]^3, {k, n}], {n, 6}] (* _Eric W. Weisstein_, May 23 2023 *)
%o A308155 (PARI) a(n)={my(s=1, d=1); for(i=2, n, d=d^2+d^3; s = 3*s + d^3); s} \\ _Andrew Howroyd_, Sep 10 2019
%Y A308155 Cf. A125295, A288796, A308134.
%K A308155 nonn
%O A308155 1,2
%A A308155 _Eric W. Weisstein_, May 14 2019
%E A308155 a(4)-a(6) from _Andrew Howroyd_, Sep 10 2019