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 A370243 #9 Feb 13 2024 07:37:39
%S A370243 1,1,7,28,143,701,3580,18376,95471,499231,2626607,13883904,73681316,
%T A370243 392323868,2094932728,11214085328,60157698287,323325959395,
%U A370243 1740682221829,9385343934124,50671846382743,273913020523933,1482311190765896,8029798017622048,43538300361416708
%N A370243 Coefficient of x^n in the expansion of ( 1/(1-x) * (1+x^2)^2 )^n.
%F A370243 a(n) = Sum_{k=0..floor(n/2)} binomial(2*n,k) * binomial(2*n-2*k-1,n-2*k).
%F A370243 The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x * (1-x) / (1+x^2)^2 ). See A369226.
%o A370243 (PARI) a(n, s=2, t=2, u=1) = sum(k=0, n\s, binomial(t*n, k)*binomial((u+1)*n-s*k-1, n-s*k));
%Y A370243 Cf. A240688, A370244.
%Y A370243 Cf. A369226.
%K A370243 nonn
%O A370243 0,3
%A A370243 _Seiichi Manyama_, Feb 13 2024