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 A368467 #25 Feb 10 2024 14:02:47
%S A368467 1,2,2,-16,-126,-498,-880,3432,37762,175916,411502,-710752,-12482928,
%T A368467 -66911830,-190616760,70959984,4208145282,26042918836,86794308524,
%U A368467 50521487200,-1397839172626,-10176550581570,-38838971577536,-51156092490048,443929768322704
%N A368467 a(n) = Sum_{k=0..n} (-1)^k * binomial(2*n,k) * binomial(4*n,n-k).
%F A368467 a(n) = [x^n] ( (1-x)^2 * (1+x)^4 )^n.
%F A368467 The g.f. exp( Sum_{k>=1} a(k) * x^k/k ) has integer coefficients and equals (1/x) * Series_Reversion( x/((1-x)^2*(1+x)^4) ). See A369190.
%o A368467 (PARI) a(n) = sum(k=0, n, (-1)^k * binomial(2*n, k)*binomial(4*n, n-k));
%Y A368467 Cf. A234839, A370106.
%Y A368467 Cf. A369190.
%K A368467 sign
%O A368467 0,2
%A A368467 _Seiichi Manyama_, Feb 10 2024