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 A068199 #15 Feb 02 2024 16:33:27
%S A068199 1,2,6,24,114,618,3732,24702,177126,1363740,11195286,97437138,
%T A068199 894857712,8637708858,87333790686,922203924216,10144109299146,
%U A068199 115972625504994,1375221840671220,16884112119546534,214270296662325534,2806600053170775372,37892025089041181982
%N A068199 One of a family of sequences that interpolates between the Bell numbers and the factorials.
%D A068199 G. Labelle et al., Stirling numbers interpolation using permutations with forbidden subsequences, Discrete Math. 246 (2002), 177-195.
%F A068199 E.g.f.: 1 + 2*exp(3exp(x)-3).
%p A068199 g:= proc(n) option remember; `if`(n=0, 1,
%p A068199 (1+add(binomial(n-1, k-1)*g(n-k), k=1..n-1))*3)
%p A068199 end:
%p A068199 a:= n-> `if`(n=0, 1, 2*g(n-1)):
%p A068199 seq(a(n), n=0..25); # _Alois P. Heinz_, Oct 09 2008
%t A068199 a[n_] := 2*BellB[n-1, 3]; a[0] = 1; Table[a[n], {n, 0, 20}] (* _Jean-François Alcover_, Nov 28 2014 *)
%Y A068199 Cf. A000110, A001861, this, A068200, A068201, ..., A000142.
%Y A068199 Equals 2 * A027710(n).
%K A068199 nonn
%O A068199 0,2
%A A068199 _N. J. A. Sloane_, Mar 23 2002
%E A068199 More terms from _Alois P. Heinz_, Oct 09 2008