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 A381778 #7 Mar 07 2025 10:47:44
%S A381778 1,2,9,60,474,4105,37681,360122,3545320,35705553,366126614,3809497971,
%T A381778 40119258081,426829897847,4580629916321,49527776299522,
%U A381778 539025763347730,5900193301962178,64913644702760248,717433047054489969,7961616716665723173,88679610762886209459
%N A381778 G.f. A(x) satisfies A(x) = (1 + x*A(x)) * C(x*A(x)^2), where C(x) is the g.f. of A000108.
%F A381778 a(n) = Sum_{k=0..n} binomial(n+3*k+1,k) * binomial(n+k+1,n-k)/(n+3*k+1).
%o A381778 (PARI) a(n) = sum(k=0, n, binomial(n+3*k+1, k)*binomial(n+k+1, n-k)/(n+3*k+1));
%Y A381778 Cf. A054727, A381779.
%Y A381778 Cf. A000108.
%K A381778 nonn
%O A381778 0,2
%A A381778 _Seiichi Manyama_, Mar 07 2025