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 A086985 #16 Mar 08 2025 02:30:06
%S A086985 0,0,0,144,6000,198000,6420960,218453760,7988440320,316674489600,
%T A086985 13630070361600,635880851020800,32050874586931200,1738651147833600000,
%U A086985 101100246720625152000,6277170099060596736000,414620927349422137344000
%N A086985 a(n) = A000407(n) - A086984(n).
%F A086985 a(n) = (2*n-1)!/(n-1)! - n! - Sum_{i=2..n} binomial(n-1, n-i)*n*n!.
%F A086985 a(n) = (2*n-1)!/(n-1)! - n! - (2^(n-1) - 1)*n*n!. - _Stefano Spezia_, Mar 07 2025
%t A086985 a[n_]:=(2*n-1)!/(n-1)!-n!-(2^(n-1)-1)*n*n!; Array[a,17] (* _Stefano Spezia_, Mar 07 2025 *)
%o A086985 (PARI) a(n)=(2*n-1)!/(n-1)!-n!-sum(i=2,n,binomial(n-1,n-i)*n*n!)
%Y A086985 Cf. A000407, A086984.
%K A086985 nonn
%O A086985 1,4
%A A086985 _Jon Perry_, Jul 27 2003