OFFSET
0,2
REFERENCES
G. Labelle et al., Stirling numbers interpolation using permutations with forbidden subsequences, Discrete Math. 246 (2002), 177-195.
FORMULA
E.g.f.: 1 + 2*exp(3exp(x)-3).
MAPLE
g:= proc(n) option remember; `if`(n=0, 1,
(1+add(binomial(n-1, k-1)*g(n-k), k=1..n-1))*3)
end:
a:= n-> `if`(n=0, 1, 2*g(n-1)):
seq(a(n), n=0..25); # Alois P. Heinz, Oct 09 2008
MATHEMATICA
a[n_] := 2*BellB[n-1, 3]; a[0] = 1; Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Nov 28 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Mar 23 2002
EXTENSIONS
More terms from Alois P. Heinz, Oct 09 2008
STATUS
approved