|
|
A112289
|
|
Denominator of sum{k=1 to n} 1/s(n,k), where s(n,k) is an unsigned Stirling number of the first kind.
|
|
2
|
|
|
1, 1, 6, 33, 4200, 4192200, 1705200, 77892963984, 10086416728304192640, 126556188275836361347200, 451535899566923284351392000, 1253032399528279799996000622278320876800
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
LINKS
|
|
|
EXAMPLE
|
a(4) = 33, the denominator of 1/6 + 1/11 + 1/6 + 1 = 47/33.
The first few fractions are: 1, 2, 11/6, 47/33, 4999/4200.
|
|
MAPLE
|
with(combinat): a:=n->denom(sum(1/abs(stirling1(n, k)), k=1..n)): seq(a(n), n=1..14); # Emeric Deutsch, Sep 02 2005
|
|
MATHEMATICA
|
f[n_] := Sum[1/Abs[StirlingS1[n, k]], {k, n}]; Table[Denominator[f[n]], {n, 15}] (* Ray Chandler, Sep 02 2005 *)
|
|
PROG
|
(PARI) a(n) = denominator(sum(k=1, n, 1/abs(stirling(n, k, 1)))); \\ Michel Marcus, Aug 17 2019
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,frac
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|