A080651 - OEIS

%I #18 Dec 31 2019 20:04:21

%S 1,3,5,6,7,8,10,11,13,14,17,22,23,26,29,34,43,47,83,94,131,137,359,

%T 431,433,449,509,569,571,2971,4723,5387,9311,9677,14431

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

%C Except for A001605(2) = 4, all terms of A001605 are terms of this sequence. - _Chai Wah Wu_, Dec 30 2019

%H Blair Kelly, <a href="http://mersennus.net/fibonacci/">Fibonacci and Lucas Factorizations</a>.

%F a(n) = A001605(n-8) for n >= 21 (conjectured). - _Chai Wah Wu_, Dec 30 2019

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

%o (PARI) isok(n) = numdiv(n) == numdiv(fibonacci(n)); \\ _Michel Marcus_, Feb 25 2016

%Y Cf. A001605, A063375.

%K nonn,more

%O 1,2

%A _Joseph L. Pe_, Feb 28 2003

%E More terms from _Ryan Propper_, May 31 2006

%E a(30)-a(34) from _Chai Wah Wu_, Dec 30 2019

%E a(35) from _Chai Wah Wu_, Dec 31 2019