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A056042 a(n) = n!/(k!)^2, where k is the largest number such that (k!)^2 divides n!. 3
1, 2, 6, 6, 30, 20, 140, 70, 630, 7, 77, 924, 12012, 3432, 51480, 12870, 218790, 48620, 923780, 184756, 3879876, 705432, 16224936, 2704156, 67603900, 10400600, 280816200, 178296, 5170584, 155117520, 4808643120, 601080390, 19835652870 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Least integer of the form n!/{(n-k)!}^2.

Similar to but different from A001405.

LINKS

Ivan Neretin, Table of n, a(n) for n = 1..1000

EXAMPLE

E.g. for n=9, 10, 11, 12, a(n)=630, 7, 77, 924 while the corresponding central binomial coefficients are 126, 252, 462, 924 respectively.

MATHEMATICA

f[n_] := Min[ Select[ Table[ n!/(n - k)!^2, {k, n}], IntegerQ[ # ] &]]; Table[ f[n], {n, 33}] (Robert G. Wilson v)

CROSSREFS

Cf. A000142, A001405, A000188, A055772, A096123, A096125.

Sequence in context: A216850 A070889 A072744 * A056040 A099566 A147299

Adjacent sequences:  A056039 A056040 A056041 * A056043 A056044 A056045

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 25 2000

STATUS

approved

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Last modified February 21 01:03 EST 2019. Contains 320362 sequences. (Running on oeis4.)