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 A238115 #20 Dec 13 2024 12:39:11
%S A238115 1,6,32,182,1117,7280,49625,349998,2535077,18758264,141254654,
%T A238115 1079364104,8350678169,65298467486,515349097712,4100346740510,
%U A238115 32858696386765,265001681344568,2149447880547398,17524254766905368,143540915998174577,1180736721910617182
%N A238115 Number of states arising in matrix method for enumerating Hamiltonian cycles on a 2n X 2n grid.
%H A238115 Andrew Howroyd, <a href="/A238115/b238115.txt">Table of n, a(n) for n = 1..500</a>
%H A238115 Ed Wynn, <a href="http://arxiv.org/abs/1402.0545">Enumeration of nonisomorphic Hamiltonian cycles on square grid graphs</a>, arXiv preprint arXiv:1402.0545 [math.CO], 2014.
%F A238115 From _Andrew Howroyd_, Dec 13 2024: (Start)
%F A238115 a(n) = Sum_{k=1..n} binomial(n,k)^2 * A000108(k).
%F A238115 a(n) = A086618(n) - 1. (End)
%p A238115 a := n -> hypergeom([1/2, -n, -n], [1, 2], 4) - 1:
%p A238115 seq(simplify(a(n)), n = 1..22); # _Peter Luschny_, Dec 13 2024
%o A238115 (PARI) a(n)=sum(k=1,n,binomial(n,k)^2*binomial(2*k,k)/(k+1)) \\ _Andrew Howroyd_, Dec 13 2024
%Y A238115 Cf. A000108, A003763, A086618, A143246, A209077, A222065, A238116, A238117, A238118.
%K A238115 nonn
%O A238115 1,2
%A A238115 _N. J. A. Sloane_, Mar 05 2014