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 A129981 #10 Aug 18 2015 00:40:14
%S A129981 1,2,4,7,15,30,78,183,567,1512,5352,15747,61827,196962,842082,2869107,
%T A129981 13191027,47650452,233445012,888174087,4604065287,18353375862,
%U A129981 100102982262,416337125487,2378327679087,10284181259712,61295935653312
%N A129981 Sum of n!!, with n>=0.
%C A129981 Partial sums of A006882.
%e A129981 0!!=1
%e A129981 1!!=1 -> 1+1=2
%e A129981 2!!=2 -> 2+2=4
%e A129981 3!!=3 -> 4+3=7
%e A129981 4!!=8 -> 7+8=15
%e A129981 5!!=15 -> 15+15=30
%p A129981 A129981 := proc(n)
%p A129981 add(doublefactorial(m),m=0..n) ;
%p A129981 end proc: # _R. J. Mathar_, Oct 11 2011
%t A129981 s = 0; lst = {}; Do[s += n!!; AppendTo[lst, s], {n, 0, 26, 1}]; lst (* _Zerinvary Lajos_, Jul 10 2009 *)
%K A129981 easy,nonn
%O A129981 0,2
%A A129981 _Paolo P. Lava_ and _Giorgio Balzarotti_, Jun 14 2007