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 A365840 #10 Sep 20 2023 10:01:22
%S A365840 1,6,55,602,7263,93192,1247636,17230290,243669007,3511010950,
%T A365840 51361157967,760784343128,11387857096900,171988619895216,
%U A365840 2617571721008520,40105744064042626,618116513218831407,9576289414539654450,149053521972041737413
%N A365840 Expansion of (1/x) * Series_Reversion( x*(1-x)^4/(1+x)^2 ).
%F A365840 a(n) = (1/(n+1)) * Sum_{k=0..n} binomial(4*n+k+3,k) * binomial(2*(n+1),n-k).
%o A365840 (PARI) a(n) = sum(k=0, n, binomial(4*n+k+3, k)*binomial(2*(n+1), n-k))/(n+1);
%Y A365840 Cf. A032349, A365839, A365841.
%Y A365840 Cf. A278745.
%K A365840 nonn
%O A365840 0,2
%A A365840 _Seiichi Manyama_, Sep 20 2023