A174331 n such that tau(Fibonacci(n)) is a perfect square.

1, 2, 6, 8, 9, 10, 14, 18, 19, 20, 22, 26, 27, 28, 30, 31, 32, 34, 40, 41, 42, 52, 53, 55, 59, 61, 64, 66, 71, 73, 74, 77, 79, 85, 87, 89, 92, 93, 94, 95, 97, 99, 101, 107, 109, 113, 115, 116, 117, 120, 121, 123, 125, 127, 128, 129, 130, 133, 135, 138, 143, 146, 147, 149

Offset: 1

Author

Michel Lagneau, Mar 15 2010

Keywords

• nonn

Comments

tau = A000005 is the number of divisors of n.

Examples

			40 is in the sequence because tau(Fibonacci(40)) = tau(102334155) = 64 is square.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..423

Crossrefs

Cf. A000005, A000045, A000290, A036436, A063375.

Programs

Mathematica

Select[Range[150], IntegerQ[Sqrt[DivisorSigma[0,Fibonacci[#]]]] &]

PARI

is(n) = issquare(numdiv(fibonacci(n))) \\ Felix Fröhlich, Sep 08 2019

Formula

{n: A063375(n) in A000290}. - R. J. Mathar, Jul 09 2012