A193348 Number of odd divisors of tau(n).

1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 2, 1, 2, 2, 3

Offset

1,4

Comments

a(n) = A001227(A000005(n)). [Reinhard Zumkeller, Jul 25 2011]

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Example

a(36) = 3 because tau(36) = 9 and the 3 odd divisors are {1, 3, 9}.

Mathematica

f[n_] := Block[{d = Divisors[DivisorSigma[0, n]]}, Count[OddQ[d], True]]; Table[f[n], {n, 80}]

Prog

(PARI) a(n)=sumdiv(sigma(n, 0), d, d%2);
(PARI) a(n)=n=numdiv(n); numdiv(n>>valuation(n, 2)) \\ Charles R Greathouse IV, Jul 30 2011

Crossrefs

Cf. A000005.

Sequence in context: A294932 A327804 A056624 * A263723 A354974 A357135

Adjacent sequences: A193345 A193346 A193347 * A193349 A193350 A193351

Keyword

nonn,easy

Author

Michel Lagneau, Jul 23 2011

Status

approved