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 A275540 #7 Aug 11 2016 17:00:36
%S A275540 1,0,1,5,27,129,761,5137,40695,363815,3632629,39927183,479047667,
%T A275540 6227155921,87178936305,1307676395009,20922800209903,355687462555407,
%U A275540 6402373891522541,121645101063561055,2432902011892531179
%N A275540 a(n) = n! + n!! - n - 1.
%t A275540 Table[n! + n!! - n - 1, {n, 0, 20}] (* _Bruno Berselli_, Aug 11 2016 *)
%Y A275540 Cf. A006882, A110903, A128882.
%K A275540 nonn,easy
%O A275540 0,4
%A A275540 _Olivier Gérard_, Aug 01 2016