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 A381912 #12 Mar 10 2025 09:42:46
%S A381912 1,3,17,124,1038,9470,91586,923542,9608323,102403921,1112500651,
%T A381912 12275235274,137193964646,1549964417407,17672282336488,
%U A381912 203092563108610,2350061579393077,27357919380212638,320186582453226290,3765185566095185740,44465070300433434901,527131055014319691537
%N A381912 Expansion of (1/x) * Series_Reversion( x * (1-x)^2 / B(x) ), where B(x) is the g.f. of A001764.
%F A381912 G.f. A(x) satisfies A(x) = B(x*A(x)) / (1 - x*A(x))^2.
%F A381912 a(n) = Sum_{k=0..n} binomial(n+3*k+1,k) * binomial(3*n-k+1,n-k)/(n+3*k+1).
%o A381912 (PARI) a(n) = sum(k=0, n, binomial(n+3*k+1, k)*binomial(3*n-k+1, n-k)/(n+3*k+1));
%Y A381912 Cf. A381911, A381913.
%Y A381912 Cf. A381879, A381915.
%Y A381912 Cf. A001764.
%K A381912 nonn
%O A381912 0,2
%A A381912 _Seiichi Manyama_, Mar 10 2025