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 A166677 #18 Jan 26 2023 10:10:40
%S A166677 1,5,18,66,280,1420,8544,59836,478720,4308516,43085200,473937244,
%T A166677 5687246976,73934210740,1035078950416,15526184256300,248418948100864,
%U A166677 4223122117714756,76016198118865680,1444307764258447996
%N A166677 a(n)= n*(a(n-1)+4), a(0)=1.
%H A166677 G. C. Greubel, <a href="/A166677/b166677.txt">Table of n, a(n) for n = 0..200</a>
%F A166677 a(n) = n!+4*floor(e*n!)-4, n>0. [_Gary Detlefs_, Jun 06 2010]
%F A166677 From _Robert Israel_, May 22 2016: (Start)
%F A166677 a(n) = n!*(1 + Sum_{k=0..n-1} 4/k!) = n! + 4 e n Gamma(n,1).
%F A166677 E.g.f.: (1+4*x*exp(x))/(1-x). (End)
%p A166677 f:= gfun:-rectoproc({a(n)=n*(a(n-1)+4),a(0)=1},a(n),remember):
%p A166677 map(f, [$0..30]); # _Robert Israel_, May 22 2016
%t A166677 FoldList[#1*#2 + 4 #2 &, 1, Range[19]] (* _Robert G. Wilson v_, Jul 07 2012 *)
%Y A166677 Cf. A000142, A033540, A165792, A165813
%K A166677 easy,nonn
%O A166677 0,2
%A A166677 _Philippe Deléham_, Oct 18 2009