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A038043 Number of ways to partition a labeled set into 2-colored subsets of equal size. 0
2, 4, 4, 10, 4, 54, 4, 284, 564, 2146, 4, 64068, 4, 273706, 3055056, 9322174, 4, 455865986, 4, 7379708912, 72557376324, 27499326586, 4, 28169911778038, 10389345718756, 15811717561854, 5955168301010504, 26845490776452304, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..29.

FORMULA

Sum { d divides n } ((2*n!)/(d!((n/d)!)^d)).

MAPLE

with(numtheory): for n from 1 to 50 do d := divisors(n): s := 0: for k from 1 to nops(d) do s := s +(2*n!)/(d[k]!*((n/d[k])!)^d[k]) od: printf(`%d, `, s) od:

CROSSREFS

Sequence in context: A253827 A186987 A300549 * A126138 A247570 A054764

Adjacent sequences:  A038040 A038041 A038042 * A038044 A038045 A038046

KEYWORD

nonn

AUTHOR

Christian G. Bower

EXTENSIONS

More terms from James A. Sellers, Feb 19 2001

STATUS

approved

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Last modified July 5 23:36 EDT 2020. Contains 335475 sequences. (Running on oeis4.)