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 A292778 #8 Dec 14 2019 19:23:45
%S A292778 1,1,3,8,25,73,234,717,2357,7480,25289,82837,289518,980017,3566993,
%T A292778 12526980,47916421,175536777,712276698,2736099789,11863097885,
%U A292778 47932689416,222692658177,946323358837,4700880455462,20946375415505,110626016074953,514550968010964
%N A292778 INVERT transform of double factorials.
%H A292778 Alois P. Heinz, <a href="/A292778/b292778.txt">Table of n, a(n) for n = 0..807</a>
%F A292778 G.f.: 1 / (1 - Sum_{k>=1} k!! * x^k). - _Ilya Gutkovskiy_, Dec 14 2019
%p A292778 a:= proc(n) option remember; `if`(n=0, 1,
%p A292778 add(doublefactorial(j)*a(n-j), j=1..n))
%p A292778 end:
%p A292778 seq(a(n), n=0..30);
%Y A292778 Cf. A006882, A051296.
%K A292778 nonn
%O A292778 0,3
%A A292778 _Alois P. Heinz_, Sep 22 2017