login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A195208 Number of odd divisors of !n. 2
1, 0, 1, 1, 3, 2, 4, 6, 8, 8, 10, 4, 6, 12, 8, 4, 24, 4, 8, 24, 32, 16, 24, 96, 32, 48, 24, 16, 384, 32, 64, 144, 16, 8, 36, 128, 16, 80, 24, 16, 96, 32, 16, 96, 4, 16, 448, 128, 64, 24, 192, 48, 192, 64, 16, 96, 768, 32, 96, 32, 64 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

!k is a subfactorial number (A000166).

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  odd divisors  1, 3, 9, 103, 309 and 927 => 6 is in the sequence.

MATHEMATICA

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

PROG

(PARI) a(n)=if(n<2, 1-n, my(x='x, k=n!*polcoeff(exp(-x+x*O(x^n))/(1-x), n)); numdiv(k>>valuation(k, 2))) \\ Charles R Greathouse IV, Sep 13 2011

CROSSREFS

Cf. A000166, A195207.

Sequence in context: A254052 A105746 A166309 * A114651 A240539 A138245

Adjacent sequences:  A195205 A195206 A195207 * A195209 A195210 A195211

KEYWORD

nonn

AUTHOR

Michel Lagneau, Sep 13 2011

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 15 11:43 EST 2019. Contains 329999 sequences. (Running on oeis4.)