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 A337751 #9 Sep 19 2020 02:21:24
%S A337751 1,1,1,1,-23,-119,-359,-839,38641,359857,1809361,6644881,-459055079,
%T A337751 -6175146119,-43468088663,-217686301559,20051525850721,
%U A337751 352724346317281,3192296431410721,20250050516224417,-2331591425921837879,-50665325105014242839,-560439561498466178759
%N A337751 a(n) = n! * Sum_{k=0..floor(n/4)} (-1)^k / (n-4*k)!.
%H A337751 Seiichi Manyama, <a href="/A337751/b337751.txt">Table of n, a(n) for n = 0..450</a>
%F A337751 G.f.: Sum_{k>=0} (-1)^k * (4*k)! * x^(4*k) / (1 - x)^(4*k+1).
%F A337751 E.g.f.: exp(x) / (1 + x^4).
%F A337751 a(0) = a(1) = a(2) = a(3) = 1; a(n) = 1 - n * (n-1) * (n-2) * (n-3) * a(n-4).
%t A337751 Table[n! Sum[(-1)^k/(n - 4 k)!, {k, 0, Floor[n/4]}], {n, 0, 22}]
%t A337751 nmax = 22; CoefficientList[Series[Exp[x]/(1 + x^4), {x, 0, nmax}], x] Range[0, nmax]!
%o A337751 (PARI) a(n) = n!*sum(k=0, n\4, (-1)^k / (n-4*k)!); \\ _Michel Marcus_, Sep 18 2020
%Y A337751 Cf. A182386, A330045, A337749, A337750.
%K A337751 sign
%O A337751 0,5
%A A337751 _Ilya Gutkovskiy_, Sep 18 2020