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 A370242 #10 Feb 13 2024 07:36:43
%S A370242 1,2,12,74,480,3202,21756,149746,1040640,7285538,51307212,363057114,
%T A370242 2579270304,18385404546,131429288828,941857237474,6764184258560,
%U A370242 48671099313730,350799656912652,2532218940625642,18303373070813280,132462237913391362,959699439413581692
%N A370242 Coefficient of x^n in the expansion of ( 1/(1-x)^2 * (1+x^2) )^n.
%F A370242 a(n) = Sum_{k=0..floor(n/2)} binomial(n,k) * binomial(3*n-2*k-1,n-2*k).
%F A370242 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) ). See A369208.
%o A370242 (PARI) a(n, s=2, t=1, u=2) = sum(k=0, n\s, binomial(t*n, k)*binomial((u+1)*n-s*k-1, n-s*k));
%Y A370242 Cf. A288470, A370245.
%Y A370242 Cf. A240688, A369208.
%K A370242 nonn
%O A370242 0,2
%A A370242 _Seiichi Manyama_, Feb 13 2024