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 A377958 #6 Nov 12 2024 11:38:01
%S A377958 1,2,3,4,17,126,787,5048,39489,361882,3641411,39948492,478777873,
%T A377958 6226077014,87182747667,1307703873856,20922694556417,355686434950578,
%U A377958 6402375749061379,121645136562423572,2432901971620591761,51090940751194252462,1124000727777806326163
%N A377958 Expansion of e.g.f. exp(x - x^2)/(1 - x).
%F A377958 a(n) = n! * Sum_{k=0..n} binomial(n-2*k,n-k) / k!.
%F A377958 a(n) = (n+1)*a(n-1) - 3*(n-1)*a(n-2) + 2*(n-1)*(n-2)*a(n-3) for n > 2.
%o A377958 (PARI) a(n) = n!*sum(k=0, n, binomial(n-2*k, n-k)/k!);
%Y A377958 Cf. A293604, A377959, A377960.
%Y A377958 Cf. A018191.
%K A377958 nonn
%O A377958 0,2
%A A377958 _Seiichi Manyama_, Nov 12 2024