A100587 - OEIS

A100587

Number of nonempty subsets of divisors of n.

1, 3, 3, 7, 3, 15, 3, 15, 7, 15, 3, 63, 3, 15, 15, 31, 3, 63, 3, 63, 15, 15, 3, 255, 7, 15, 15, 63, 3, 255, 3, 63, 15, 15, 15, 511, 3, 15, 15, 255, 3, 255, 3, 63, 63, 15, 3, 1023, 7, 63, 15, 63, 3, 255, 15, 255, 15, 15, 3, 4095, 3, 15, 63, 127, 15, 255, 3, 63, 15, 255, 3, 4095, 3

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OFFSET

1,2

COMMENTS

A119347(n) <= a(n). - Reinhard Zumkeller, Jun 27 2015

LINKS

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

Wasin So, Integral circulant graphs, Discr. Math. 306 (1) (2006) 153-158

FORMULA

a(n) = -1 + 2^tau(n), where tau(n) = DivisorSigma(0, n) = A000005(n).

EXAMPLE

For all prime numbers p, a(p)=3, since those subsets are {{1,p},{1},{p}}.