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 A377955 #9 Nov 12 2024 09:01:52
%S A377955 1,4,15,58,241,1056,4879,23710,120033,635356,3478351,19796514,
%T A377955 115988305,703052728,4372581711,28022140486,183804777409,
%U A377955 1238244635700,8520907808143,60061024788106,431735704061361,3171780156493264,23730347517489295,181115025566445678
%N A377955 a(n) = n! * Sum_{k=0..n} binomial(k+3,n-k) / k!.
%F A377955 E.g.f.: (1 + x)^3 * exp(x + x^2).
%F A377955 a(n) = -(n-5)*a(n-1) + 3*(n-1)*a(n-2) + 2*(n-1)*(n-2)*a(n-3) for n > 2.
%o A377955 (PARI) a(n) = n!*sum(k=0, n, binomial(k+3, n-k)/k!);
%Y A377955 Cf. A018191, A047974, A377954, A377956.
%K A377955 nonn,easy
%O A377955 0,2
%A A377955 _Seiichi Manyama_, Nov 12 2024