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 A360731 #12 Feb 18 2023 19:57:52
%S A360731 1,1,4,27,257,3141,46899,827639,16855357,389100834,10040378183,
%T A360731 286386193685,8947506702834,303875954083536,11146559606379269,
%U A360731 439178938765108083,18497974976610341624,829420114454360154295,39445018962975879216867
%N A360731 Expansion of Sum_{k>=0} (k * x * (1 + k*x^3))^k.
%H A360731 Winston de Greef, <a href="/A360731/b360731.txt">Table of n, a(n) for n = 0..385</a>
%F A360731 a(n) = Sum_{k=0..floor(n/4)} (n-3*k)^(n-2*k) * binomial(n-3*k,k).
%o A360731 (PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k*x*(1+k*x^3))^k))
%o A360731 (PARI) a(n) = sum(k=0, n\4, (n-3*k)^(n-2*k)*binomial(n-3*k, k));
%Y A360731 Cf. A360618, A360730.
%K A360731 nonn
%O A360731 0,3
%A A360731 _Seiichi Manyama_, Feb 18 2023