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 A368894 #7 Jan 09 2024 08:48:06
%S A368894 1,1,-1,-5,5,56,-29,-923,-119,19855,17711,-524160,-926771,16339441,
%T A368894 45275035,-585443909,-2298643951,23626165600,124604211943,
%U A368894 -1056587815835,-7261611779179,51645640102519,455056929514067,-2724884512463520,-30595315890959975
%N A368894 a(n) = Sum_{k=0..floor(n/2)} (-n)^k * binomial(n-k,k).
%F A368894 a(n) = [x^n] 1/(1 - x + n*x^2).
%o A368894 (PARI) a(n) = sum(k=0, n\2, (-n)^k*binomial(n-k, k));
%Y A368894 Cf. A171180, A368895.
%K A368894 sign,easy
%O A368894 0,4
%A A368894 _Seiichi Manyama_, Jan 09 2024