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 A113550 #19 Aug 15 2025 10:38:36
%S A113550 1,6,6,840,120,332640,5040,259459200,362880,335221286400,39916800,
%T A113550 647647525324800,6227020800,1748648318376960000,1307674368000,
%U A113550 6288139352883548160000,355687428096000,29051203810321992499200000,121645100408832000,167683548393178540705382400000
%N A113550 a(n) = product of n successive numbers up to n, if n is odd a(n) = n*(n-1)*.. = n!, if n is even a(n) = n(n+1)(n+2)... 'n' terms.
%H A113550 G. C. Greubel, <a href="/A113550/b113550.txt">Table of n, a(n) for n = 1..350</a>
%F A113550 a(2n-1) = (2n-1)!, a(2n) = (4n-1)!/(2n-1)!.
%F A113550 a(2n-1)*a(2n) = (4n-1)!.
%F A113550 Sum_{n>=1} 1/a(n) = sinh(1) + (sqrt(Pi)/2) * (exp(1/4) * erf(1/2) - exp(-1/4) * erfi(1/2)). - _Amiram Eldar_, Aug 15 2025
%e A113550 a(3) = 3*2*1 = 6.
%e A113550 a(4) = 4*5*6*7 = 840.
%t A113550 n = 1; anfunc[n_] := (If [EvenQ[n], {an = n, Do[an = an*(n + i), {i, n - 1}]}, an = n! ]; an); Table[anfunc[n], {n, 1, 20}] (* Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006 *)
%Y A113550 Cf. A113549.
%Y A113550 Cf. A019704, A073742, A092042, A092616, A333419, A367563.
%K A113550 easy,nonn
%O A113550 1,2
%A A113550 _Amarnath Murthy_, Nov 03 2005
%E A113550 More terms from Elizabeth A. Blickley (Elizabeth.Blickley(AT)gmail.com), Mar 10 2006