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 A117735 #3 Mar 30 2012 17:34:20
%S A117735 0,0,0,0,18,90,690,4830,40110,362670,3628590,39914490,478999290,
%T A117735 6226990770,87178261170,1307674337970,20922789857970,355687427585490,
%U A117735 6402373705217490,121645100399132310,2432902008166940310
%N A117735 a(n) = n! - primorial(n).
%F A117735 a(0)=0. a(n) = n!-A034386(n) = A000142(n)-A034386(n), n>0.
%t A117735 f[n_] := If[PrimeQ[n] == True, 1, n] cf[0] = 1; cf[n_Integer?Positive] := cf[n] = f[n]*cf[n - 1] g[n_] := If[PrimeQ[n] == True, n, 1] p[0] = 1; p[n_Integer?Positive] := p[n] = g[n]*p[n - 1] Table[n! - p[n], {n, 0, 20}]
%Y A117735 Cf. A034386, A117683.
%K A117735 nonn
%O A117735 0,5
%A A117735 _Roger L. Bagula_, Apr 14 2006