A193291 Number of even divisors of Fibonacci(n).

0, 0, 1, 0, 0, 3, 0, 0, 2, 0, 0, 12, 0, 0, 4, 0, 0, 12, 0, 0, 4, 0, 0, 60, 0, 0, 8, 0, 0, 48, 0, 0, 4, 0, 0, 128, 0, 0, 4, 0, 0, 48, 0, 0, 16, 0, 0, 288, 0, 0, 4, 0, 0, 96, 0, 0, 16, 0, 0, 768, 0, 0, 16, 0, 0, 48, 0, 0, 16, 0, 0, 1280, 0, 0, 24, 0, 0, 96, 0

Offset: 1

Author

Michel Lagneau, Jul 21 2011

Keywords

• nonn

Examples

			a(6) = 3 because Fibonacci(6) = 8 and the 3 even divisors are {2, 4, 8}.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000045, A183063.

Programs

Mathematica

a[n_] := Block[{d = Divisors[Fibonacci[n]]}, Count[EvenQ[d], True]]; Table[a[n], {n, 110}]

PARI

a(n)=if(n%3,0,numdiv(fibonacci(n)/2)) \\ Charles R Greathouse IV, Jul 30 2011

Formula

a(n) = A183063(A000045(n)). - Amiram Eldar, Sep 03 2019