A112291 Denominator of sum{k=1 to n} 1/S(n,k), where S(n,k) is a Stirling number of the second kind.

1, 1, 3, 42, 150, 36270, 270900, 9440379900, 3332912051700, 2004302168707167000, 1424191116445997823000, 3936008766237071969447818200, 10888542544398564939894000, 3606055788316324023953497288103040

Offset

1,3

Links

Vaclav Kotesovec, Table of n, a(n) for n = 1..49

Example

a(4) = 42, the denominator of 1/1 + 1/7 + 1/6 + 1 = 97/42.
The first few fractions are: 1, 2, 7/3, 97/42, 331/150, 77089/36270, 562609/270900.

Maple

with(combinat): a:=n->denom(sum(1/stirling2(n, k), k=1..n)): seq(a(n), n=1..15); # Emeric Deutsch, Sep 02 2005

Mathematica

f[n_] := Sum[1/StirlingS2[n, k], {k, n}]; Table[Denominator[f[n]], {n, 15}] (* Ray Chandler, Sep 02 2005 *)

Crossrefs

Cf. A112290.

Sequence in context: A237661 A116006 A079826 * A063040 A365594 A294517

Adjacent sequences: A112288 A112289 A112290 * A112292 A112293 A112294

Keyword

nonn,frac

Author

Leroy Quet, Sep 01 2005

Extensions

Extended by Emeric Deutsch and Ray Chandler, Sep 02 2005

Status

approved