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 A256880 #10 Apr 22 2015 18:27:01 %S A256880 1,4,9,48,200,1440,8820,80640,653184,7257600,73180800,958003200, %T A256880 11564467200,174356582400,2451889440000,41845579776000, %U A256880 671854030848000,12804747411456000,231125690776780800,4865804016353280000 %N A256880 n*n!/round(n/2). %F A256880 a(2n-1) = A052145(n). %F A256880 a(2n) = 4*A002674(n) = 2*A010050(n) = 2^(n+1)*A000680(n), n>=1. %o A256880 (PARI) a(n)=n*n!/round(n/2) \\ _M. F. Hasler_, Apr 22 2015 %Y A256880 Cf. A000142, A052145. %K A256880 nonn,easy %O A256880 1,2 %A A256880 _M. F. Hasler_, Apr 21 2015