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 A113549 #11 Aug 12 2025 03:23:17
%S A113549 1,2,60,24,15120,720,8648640,40320,8821612800,3628800,14079294028800,
%T A113549 479001600,32382376266240000,87178291200,101421602465863680000,
%U A113549 20922789888000,415017197290314178560000,6402373705728000,2149789081963827444940800000
%N A113549 a(n) = product of n successive numbers up to n, if n is even a(n) = n*(n-1)*.. = n!, if n is odd a(n) = n(n+1)(n+2)... 'n' terms.
%H A113549 G. C. Greubel, <a href="/A113549/b113549.txt">Table of n, a(n) for n = 1..350</a>
%F A113549 a(1) = 1, a(2n) = (2n)!, a(2n-1) = (4n-3)!/(2n-2)!.
%F A113549 a(2n)*a(2n+1) = (4n+1)!.
%e A113549 a(3) = 3*4*5 = 60.
%e A113549 a(4) = 4*3*2*1 = 24.
%t A113549 n = 1; anfunc[n_] := (If [OddQ[n], {an = n, Do[an = an*(n + i), {i, n - 1}]}, an = n! ]; an); Table[anfunc[n], {n, 1, 19}] (* Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006 *)
%Y A113549 Cf. A113550.
%K A113549 easy,nonn
%O A113549 1,2
%A A113549 _Amarnath Murthy_, Nov 03 2005
%E A113549 More terms from Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006