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 A370245 #9 Feb 13 2024 07:39:54
%S A370245 1,2,16,110,828,6352,49696,393668,3148316,25362992,205519616,
%T A370245 1673272702,13677016932,112165564656,922490228032,7605558361960,
%U A370245 62839438825244,520180768020464,4313251202569216,35818392770702104,297846498752214128,2479748570715505472
%N A370245 Coefficient of x^n in the expansion of ( 1/(1-x)^2 * (1+x^2)^3 )^n.
%F A370245 a(n) = Sum_{k=0..floor(n/2)} binomial(3*n,k) * binomial(3*n-2*k-1,n-2*k).
%F A370245 The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x * (1-x)^2 / (1+x^2)^3 ). See A369263.
%o A370245 (PARI) a(n, s=2, t=3, u=2) = sum(k=0, n\s, binomial(t*n, k)*binomial((u+1)*n-s*k-1, n-s*k));
%Y A370245 Cf. A288470, A360242.
%Y A370245 Cf. A369263.
%K A370245 nonn
%O A370245 0,2
%A A370245 _Seiichi Manyama_, Feb 13 2024