A080651 Numbers n such that n and Fibonacci(n) have the same number of divisors.

1, 3, 5, 6, 7, 8, 10, 11, 13, 14, 17, 22, 23, 26, 29, 34, 43, 47, 83, 94, 131, 137, 359, 431, 433, 449, 509, 569, 571, 2971, 4723, 5387, 9311, 9677, 14431

Offset: 1

Author

Joseph L. Pe, Feb 28 2003

Keywords

• nonn
• more

Comments

Except for A001605(2) = 4, all terms of A001605 are terms of this sequence. - Chai Wah Wu, Dec 30 2019

Links

• Blair Kelly, Fibonacci and Lucas Factorizations.

Crossrefs

Cf. A001605, A063375.

Programs

Mathematica

Select[Range[2*10^2], DivisorSigma[0, Fibonacci[ # ]] == DivisorSigma[0, # ] &]

PARI

isok(n) = numdiv(n) == numdiv(fibonacci(n)); \\ Michel Marcus, Feb 25 2016

Formula

a(n) = A001605(n-8) for n >= 21 (conjectured). - Chai Wah Wu, Dec 30 2019

Extensions

More terms from Ryan Propper, May 31 2006

a(30)-a(34) from Chai Wah Wu, Dec 30 2019

a(35) from Chai Wah Wu, Dec 31 2019