A261609 - OEIS

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A261609

Number of composite divisors of n^2+1.

1

0, 0, 1, 0, 1, 0, 3, 1, 1, 0, 1, 1, 4, 0, 1, 0, 4, 3, 1, 0, 4, 1, 4, 0, 1, 0, 4, 1, 1, 1, 4, 3, 4, 1, 1, 0, 4, 3, 1, 0, 3, 1, 8, 1, 1, 1, 11, 1, 1, 1, 1, 1, 4, 0, 4, 0, 12, 1, 1, 1, 1, 1, 4, 1, 1, 0, 4, 5, 1, 3, 1, 4, 11, 0, 4, 1, 4, 1, 1, 1, 4, 3, 11, 0, 1, 1

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OFFSET

1,7

LINKS

Michel Lagneau, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A055212(A002522(n)).

EXAMPLE

a(7) = 3 because the composite divisors of 7^2+1 are 10, 25, 50.

MATHEMATICA

Table[ Count[ PrimeQ[ Divisors[n^2+1] ], False] - 1, {n, 1, 105} ]

CROSSREFS

Cf. A002522, A055212, A128428, A193330, A193432.

Sequence in context: A193140 A319993 A122776 * A228488 A338638 A062172

Adjacent sequences: A261606 A261607 A261608 * A261610 A261611 A261612

KEYWORD

nonn,easy

AUTHOR

Michel Lagneau, Aug 26 2015

STATUS

approved