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 A379171 #11 Dec 17 2024 10:12:31
%S A379171 1,4,21,139,1021,8010,65708,556751,4834686,42800265,384832083,
%T A379171 3504693519,32261240127,299685628629,2805773759322,26448278629697,
%U A379171 250806022116194,2390973659474304,22901157688878983,220279614235505630,2126890041331033797,20606993367985131716
%N A379171 G.f. A(x) satisfies A(x) = (1 + x)/(1 - x*A(x))^3.
%F A379171 a(n) = Sum_{k=0..n} binomial(n-k+1,k) * binomial(4*n-4*k+2,n-k)/(n-k+1).
%o A379171 (PARI) a(n) = sum(k=0, n, binomial(n-k+1, k)*binomial(4*n-4*k+2, n-k)/(n-k+1));
%Y A379171 Cf. A365764, A369215, A379172.
%Y A379171 Cf. A025227, A379173.
%K A379171 nonn
%O A379171 0,2
%A A379171 _Seiichi Manyama_, Dec 17 2024