OFFSET
1,1
COMMENTS
From Robert Israel, Aug 18 2015: (Start)
Numbers n such that A022307(n) = 13.
If n is in the sequence, then k*n is not in the sequence for k > 1.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..54
Blair Kelly, Fibonacci and Lucas Factorizations.
EXAMPLE
a(1)=120 because the 120th Fibonacci number consists of 13 distinct prime factors (i.e., 5358359254990966640871840 = 2^5 * 3^2 * 5 * 7 * 11 * 23 * 31 * 41 * 61 * 241 * 2161 * 2521 * 20641).
MAPLE
select(t -> nops(numtheory:-factorset(combinat:-fibonacci(t)))=13, [$1..1000]); # Robert Israel, Aug 10 2015
MATHEMATICA
Select[Range[1250], PrimeNu[Fibonacci[#]]==13&] (* Harvey P. Dale, Apr 30 2015 *)
PROG
(PARI) n=1; while(n<265, if(omega(fibonacci(n))==13, print1(n, ", ")); n++)
(SageMath)
for n in range(1, 3*10^2):
if len(prime_factors(fibonacci(n)))==13:
print(n) # Manfred Scheucher, Aug 04 2015
(Magma) [n: n in [1..3*10^2] |(#(PrimeDivisors(Fibonacci(n)))) eq 13]; // Vincenzo Librandi, Aug 05 2015
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Shyam Sunder Gupta, Feb 19 2006
EXTENSIONS
More terms from Ryan Propper, Apr 26 2006
a(36)-a(45) from Max Alekseyev, Aug 18 2013
a(46)-a(50) from Amiram Eldar, Oct 14 2019
STATUS
approved