OFFSET
1,1
COMMENTS
Has many terms in common with A023172 (41 below 1000), but neither is a subsequence of the other since 125 is not in this sequence.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..212
Blair Kelly, Fibonacci and Lucas Factorizations.
FORMULA
a(n) = {k: tau(Fibonacci(k)) != 2^i for all i}.
EXAMPLE
F(12) = 144 has 15 divisors: {1, 2, 3, 4, 6, 8, 9, 12, 16, 18, 24, 36, 48, 72, 144}. Since 15 is not a power of 2, 12 is in the sequence.
F(24) = 46368 has 72 divisors. Since 72 is not a power of 2, 24 is in the sequence.
MATHEMATICA
Do[If[ !IntegerQ[Log[2, DivisorSigma[0, Fibonacci[n]]]], Print[n]], {n, 10^3}]
PROG
(PARI) is(k) = {my(d = numdiv(fibonacci(k))); d >> valuation(d, 2) > 1; } \\ Amiram Eldar, Aug 12 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Ryan Propper, Jun 01 2006
STATUS
approved