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 A110903 #13 May 09 2024 13:26:35
%S A110903 0,0,0,3,16,105,672,4935,39936,361935,3624960,39906405,478955520,
%T A110903 6226885665,87177646080,1307672340975,20922779566080,355687393636575,
%U A110903 6402373519933440,121645099754102925,2432902004460748800,51090942157960129425,1124000727695858073600
%N A110903 Difference between the factorial of n and the double factorial of n.
%H A110903 Andrew Howroyd, <a href="/A110903/b110903.txt">Table of n, a(n) for n = 0..200</a>
%F A110903 a(n) = n! - n!!.
%F A110903 a(n) = A000142(n) - A006882(n). - _Andrew Howroyd_, Jan 02 2020
%e A110903 a(7) = 7*6*5*4*3*2*1 - 7*5*3*1 = 4935.
%t A110903 Table[(n!-n!!), {n,0, 15}] (* _Zerinvary Lajos_, Mar 21 2007 *)
%o A110903 (PARI) a(n)={n! - if(n%2, n!/((n\2)!*2^(n\2)), (n/2)!*2^(n/2))} \\ _Andrew Howroyd_, Jan 02 2020
%Y A110903 Cf. A000142 (factorials), A006882 (double factorials).
%K A110903 easy,nonn
%O A110903 0,4
%A A110903 _Paolo P. Lava_, Sep 21 2005
%E A110903 Terms a(15) and beyond from _Andrew Howroyd_, Jan 02 2020