A347001 Expansion of e.g.f. exp( log(1 - x)^2 / 2 ).

1, 0, 1, 3, 14, 80, 544, 4284, 38310, 383256, 4239006, 51345690, 675770028, 9600349824, 146396925648, 2384700728760, 41320373582652, 758780222426592, 14718569154071964, 300706641183038292, 6453691377726073128, 145154958710291611200, 3414131149418742544320

Offset

0,4

Links

Seiichi Manyama, Table of n, a(n) for n = 0..448

Formula

a(0) = 1; a(n) = Sum_{k=1..n} binomial(n-1,k-1) * |Stirling1(k,2)| * a(n-k).

a(n) = Sum_{k=0..floor(n/2)} (2*k)! * |Stirling1(n,2*k)|/(2^k * k!). - Seiichi Manyama, May 06 2022

Mathematica

nmax = 22; CoefficientList[Series[Exp[Log[1 - x]^2/2], {x, 0, nmax}], x] Range[0, nmax]!
a[0] = 1; a[n_] := a[n] = Sum[Binomial[n - 1, k - 1] Abs[StirlingS1[k, 2]] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 22}]

Prog

(PARI) a(n) = sum(k=0, n\2, (2*k)!*abs(stirling(n, 2*k, 1))/(2^k*k!)); \\ Seiichi Manyama, May 06 2022

Crossrefs

Cf. A000254, A060311, A305306, A346921, A347002, A347003, A347004.

Sequence in context: A000264 A009053 A202474 * A354325 A346966 A256336

Adjacent sequences: A346998 A346999 A347000 * A347002 A347003 A347004

Keyword

nonn

Author

Ilya Gutkovskiy, Aug 10 2021

Status

approved