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 A372139 #8 Apr 20 2024 10:27:54
%S A372139 1,1,5,22,131,775,5018,33066,225915,1569663,11114665,79715150,
%T A372139 578603008,4239698240,31329174328,233166912152,1746351112863,
%U A372139 13152340002195,99545267265903,756752801436930,5775810585852675,44241685802126865,339991810347999194
%N A372139 G.f. A(x) satisfies A(x) = 1/( 1 - x * (1 + 4*x)^(1/2) * A(x)^2 ).
%F A372139 a(n) = Sum_{k=0..n} 4^(n-k) * binomial(3*k,k) * binomial(k/2,n-k)/(2*k+1).
%o A372139 (PARI) a(n) = sum(k=0, n, 4^(n-k)*binomial(3*k, k)*binomial(k/2, n-k)/(2*k+1));
%Y A372139 Cf. A364475, A372137.
%K A372139 nonn
%O A372139 0,3
%A A372139 _Seiichi Manyama_, Apr 20 2024