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 A117125 #3 Aug 24 2012 10:49:56 %S A117125 0,1,3,4,5,9,15,16,21,22,23,72,105,112,117,118,119,336,615,672,705, %T A117125 712,717,718,719,1200,4095,4656,4935,4992,5025,5032,5037,5038,5039 %N A117125 Positive integers that can be expressed as the difference between a factorial and a double factorial. %F A117125 n! - m!! being n! > m!! %e A117125 117 = 5! - 3!! %e A117125 4992 = 7! - 6!! %Y A117125 Cf. A110903, A111300. %K A117125 nonn %O A117125 1,3 %A A117125 _Paolo P. Lava_ and _Giorgio Balzarotti_, Apr 20 2006