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 A381938 #13 Mar 11 2025 07:54:53
%S A381938 1,3,9,52,380,3066,26304,235314,2170312,20487963,196988392,1922327792,
%T A381938 18990571724,189548947601,1908604524752,19364096602370,
%U A381938 197761735366804,2031444188437719,20974821788118024,217561484977675026,2265961977605950416,23688432825547509283
%N A381938 G.f. A(x) satisfies A(x) = (1 + x)^2 * B(x*A(x)), where B(x) is the g.f. of A001764.
%F A381938 a(n) = Sum_{k=0..n} binomial(4*k+1,k) * binomial(2*k+2,n-k)/(4*k+1).
%F A381938 a(n) = A381785(n) + A381785(n-1).
%o A381938 (PARI) a(n) = sum(k=0, n, binomial(4*k+1, k)*binomial(2*k+2, n-k)/(4*k+1));
%Y A381938 Cf. A366694, A367640, A381941.
%Y A381938 Cf. A001764, A381785.
%K A381938 nonn
%O A381938 0,2
%A A381938 _Seiichi Manyama_, Mar 10 2025