A262095 - OEIS

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A262095

Number of non-semiprime divisors of n.

1, 2, 2, 2, 2, 3, 2, 3, 2, 3, 2, 4, 2, 3, 3, 4, 2, 4, 2, 4, 3, 3, 2, 6, 2, 3, 3, 4, 2, 5, 2, 5, 3, 3, 3, 6, 2, 3, 3, 6, 2, 5, 2, 4, 4, 3, 2, 8, 2, 4, 3, 4, 2, 6, 3, 6, 3, 3, 2, 8, 2, 3, 4, 6, 3, 5, 2, 4, 3, 5, 2, 9, 2, 3, 4, 4, 3, 5, 2, 8, 4, 3, 2, 8, 3, 3, 3, 6, 2, 8, 3, 4, 3, 3, 3, 10, 2

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OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A000005(n) - A086971(n).

A083399(n) <= a(n) <= A000005(n).

a(n) = Sum_{k=1..A000005(n)} (1 - A064911(A027750(n,k))). - Reinhard Zumkeller, Sep 14 2015

EXAMPLE

(1, 2, 3, 4, 6, 8, 12, 24) are the divisors of n = 24: 1, 2, 3, 8, 12, and 24 are non-semiprimes, therefore a(24) = 6.

MATHEMATICA