A305547 - OEIS

%I #74 Oct 04 2020 03:39:35

%S 1,1,2,8,37,182,1039,7149,56382,479220,4280247,40406984,410453366,

%T 4539623168,54431372233,695801259947,9312538336475,128985882874288,

%U 1842668013046405,27238267120063415,419396473955088310,6769168354222927254,114837651830425810381,2042782103293394499566

%N Expansion of e.g.f. Product_{k>=1} (1 + (exp(x) - 1)^k/k!).

%C Stirling transform of A007837.

%H Seiichi Manyama, <a href="/A305547/b305547.txt">Table of n, a(n) for n = 0..500</a>

%H N. J. A. Sloane, <a href="/transforms.txt">Transforms</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/StirlingTransform.html">Stirling Transform</a>

%F E.g.f.: exp(Sum_{k>=1} Sum_{j>=1} (-1)^(k+1)*(exp(x) - 1)^(j*k)/((j!)^k*k)).

%F a(n) = Sum_{k=0..n} Stirling2(n,k)*A007837(k).

%p b:= proc(n) option remember; `if`(n=0, 1, add(add((-d)*(-d!)^(-k/d),

%p        d=numtheory[divisors](k))*(n-1)!/(n-k)!*b(n-k), k=1..n))

%p     end:

%p a:= n-> add(Stirling2(n, k)*b(k), k=0..n):

%p seq(a(n), n=0..25);  # _Alois P. Heinz_, Jun 15 2018

%t nmax = 23; CoefficientList[Series[Product[(1 + (Exp[x] - 1)^k/k!), {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]!

%t nmax = 23; CoefficientList[Series[Exp[Sum[Sum[(-1)^(k + 1) (Exp[x] - 1)^(j k)/((j!)^k k), {j, 1, nmax}], {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]!

%t b[0] = 1; b[n_] := b[n] = Sum[(n - 1)!/(n - k)! DivisorSum[k, -# (-#!)^(-k/#) &] b[n - k], {k, 1, n}]; a[n_] := a[n] = Sum[StirlingS2[n, k] b[k], {k, 0, n}]; Table[a[n], {n, 0, 23}]

%Y Cf. A007837, A140585, A305987.

%K nonn

%O 0,3

%A _Ilya Gutkovskiy_, Jun 15 2018