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A195207 Number of even divisors of !n. 2
0, 0, 0, 1, 0, 4, 0, 6, 0, 24, 0, 4, 0, 24, 0, 4, 0, 16, 0, 24, 0, 32, 0, 96, 0, 144, 0, 16, 0, 64, 0, 144, 0, 40, 0, 128, 0, 160, 0, 16, 0, 96, 0, 96, 0, 32, 0, 128, 0, 96, 0, 48, 0, 128, 0, 96, 0, 96, 0, 32, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

!n is a subfactorial number (A000166).

Property of this sequence : for n different of 3, the number of even divisors of !n seems even.

LINKS

Table of n, a(n) for n=0..60.

EXAMPLE

a(7) = 6 because the divisors of  !7 = 1854 are  {1, 2, 3, 6, 9, 18, 103, 206, 309, 618, 927, 1854}with 6  even divisors  2, 6, 18, 206, 618, 1854 => 6 is in the sequence.

MATHEMATICA

f[n_] := Block[{d = Divisors[Subfactorial[n]]}, Count[EvenQ[d], True]]; Table[f[n], {n, 0, 60}]

CROSSREFS

Cf. A000166, A195208.

Sequence in context: A023891 A075091 A132953 * A157721 A085968 A010637

Adjacent sequences:  A195204 A195205 A195206 * A195208 A195209 A195210

KEYWORD

nonn

AUTHOR

Michel Lagneau, Sep 13 2011

STATUS

approved

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Last modified December 9 22:27 EST 2019. Contains 329880 sequences. (Running on oeis4.)