A261609 Number of composite divisors of n^2+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

Offset: 1

Author

Michel Lagneau, Aug 26 2015

Keywords

• nonn
• easy

Examples

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

Links

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

Crossrefs

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

Programs

Mathematica

Table[ Count[ PrimeQ[ Divisors[n^2+1] ], False] - 1, {n, 1, 105} ]
Table[Count[Divisors[n^2+1],?CompositeQ],{n,100}] (* _Harvey P. Dale, Dec 16 2024 *)

Formula

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