A083019 - OEIS

%I #19 Jun 09 2022 06:32:19

%S 1,1,1,1,2,2,1,1,1,2,1,6,1,1,2,1,1,2,1,2,1,1,1,8,3,1,1,1,1,4,1,1,1,1,

%T 2,9,1,1,1,2,1,2,1,1,2,1,1,10,1,3,1,1,1,2,2,2,1,1,1,12,1,1,1,1,2,2,1,

%U 1,1,2,1,12,1,1,3,1,1,2,1,2,1,1,1,6,2,1,1,1,1,4,2,1,1,1,2,12,1,1,1,3,1,2,1

%N Number of common divisors of n and F(n) where F(n) denotes the n-th Fibonacci number.

%H Amiram Eldar, <a href="/A083019/b083019.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000005(A104714(n)). - _Amiram Eldar_, Jun 09 2022

%t Table[Length[Intersection[Divisors[n],Divisors[Fibonacci[n]]]],{n,120}] (* _Harvey P. Dale_, Aug 24 2014 *)

%t a[n_] := DivisorSigma[0, GCD[n, Fibonacci[n]]]; Array[a, 100] (* _Amiram Eldar_, Oct 18 2019 *)

%o (PARI) a(n) = length(setintersect(divisors(n), divisors(fibonacci(n)))); \\ _Michel Marcus_, Dec 04 2013

%Y Cf. A000005, A000045, A104714.

%K nonn,easy

%O 1,5

%A _Benoit Cloitre_, May 31 2003