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 A353014 #17 Apr 16 2022 09:34:29
%S A353014 1,1,4,27,257,3133,46737,824568,16792857,387700668,10005768898,
%T A353014 285445966496,8919588913002,302975146962245,11115146328067250,
%U A353014 438000914977377939,18450682450377791691,827395864513198608177,39352977767853205024131
%N A353014 a(n) = Sum_{k=0..floor(n/3)} (n-3*k)^(n-2*k).
%F A353014 G.f.: Sum_{k>=0} (k * x)^k / (1 - k * x^3).
%t A353014 a[0] = 1; a[n_] := Sum[(n - 3*k)^(n - 2*k), {k, 0, Floor[n/3]}]; Array[a, 20, 0] (* _Amiram Eldar_, Apr 16 2022 *)
%o A353014 (PARI) a(n) = sum(k=0, n\3, (n-3*k)^(n-2*k));
%o A353014 (PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=0, N, (k*x)^k/(1-k*x^3)))
%Y A353014 Cf. A031971, A353013.
%Y A353014 Cf. A352946, A353015.
%K A353014 nonn,easy
%O A353014 0,3
%A A353014 _Seiichi Manyama_, Apr 16 2022