This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A105307 #6 Apr 13 2021 23:53:06
%S A105307 0,0,1,1,1,2,1,2,2,2,1,-1,1,2,3,3,1,4,2,4,3,2,1,-1,-1,2,4,4,1,6,2,4,3,
%T A105307 2,3,-1,3,3,3,6,2,6,1,5,5,3,1,-1,3,-1,3,4,2,7,4,-1,5,3,2,-1,2,3,5,6,3,
%U A105307 6,3,5,5,7,2,-1,2,4,-1,5,4,7,2,9,7,3,1,-1,4,3,4,9,2,11,-1,6,4,2,6,-1,4,5,6,-1,2,7,3,7,7,3,2,-1,2,-1,5,-1,2,9,4,6,6,5,3
%N A105307 Base-2 logarithm of the number of divisors of Fibonacci(n) if that number is a power of 2, otherwise -1.
%C A105307 It appears that the number of divisors of most Fibonacci numbers is a power of 2.
%e A105307 F(6)=8 has 4 divisors {1,2,4,8}, so a(6) = log_2(4) = 2.
%Y A105307 Cf. A081979.
%K A105307 sign
%O A105307 1,6
%A A105307 _John W. Layman_, May 03 2005