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 A226283 #16 Jul 12 2024 16:35:51 %S A226283 0,0,0,4,36,324,2592,20736,172800,1440000,12960000,116640000, %T A226283 1143072000,11202105600,119489126400,1274550681600,14748372172800, %U A226283 170659735142400,2133246689280000,26665583616000000,358503957504000000,4819886539776000000,69406366172774400000 %N A226283 a(n) = [n/2]!*[(n+1)/2]!*C([n/2],2)*C([(n+1)/2],2). %C A226283 Number of permutations of n elements with 4 odd displacements. %C A226283 Column 3 of A226288. %C A226283 Column k=4 of A145893, a diagonal of A145894. - _Alois P. Heinz_, May 29 2014 %H A226283 R. H. Hardin, <a href="/A226283/b226283.txt">Table of n, a(n) for n = 1..210</a> %t A226283 a[n_]:=(Floor[n/2])!(Floor[(n+1)/2])!Binomial[Floor[n/2],2]Binomial[Floor[(n+1)/2],2]; Array[a,23] (* _Stefano Spezia_, Jul 12 2024 *) %Y A226283 Cf. A145893, A145894, A226288. %K A226283 nonn %O A226283 1,4 %A A226283 _R. H. Hardin_, connection of formula with combinatoric problem via _N. J. A. Sloane_ in the Sequence Fans Mailing List, Jun 02 2013