A114813 Indices of Fibonacci numbers with 4 prime factors when counted with multiplicity.

20, 27, 28, 32, 52, 55, 74, 77, 85, 87, 93, 97, 115, 123, 143, 146, 149, 157, 161, 163, 178, 187, 197, 209, 211, 214, 215, 221, 223, 239, 242, 249, 262, 269, 283, 287, 307, 311, 313, 321, 334, 349, 379, 391, 393, 409, 421, 453, 487, 493, 499, 523, 581, 586

Offset: 1

Author

Shyam Sunder Gupta, Feb 19 2006

Keywords

• nonn

Comments

1559, 1609, 2131, 2281, 2351, 2459, 2539, 3119, 3371, 4993, 5839, 6217, 7591, 7741, 8353, 9931 are also terms (data from Kelly link). - Chai Wah Wu, Nov 11 2019

Examples

			a(1)=20 because 20th Fibonacci number (i.e., 6765) consists of 4 prime factors (i.e., 3*5*11*41).
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..86
• Blair Kelly, Fibonacci and Lucas Factorizations.

Crossrefs

Column k=4 of A303215.

Programs

Mathematica

t = {}; Do[f = FactorInteger[Fibonacci[n]]; If[Total[Transpose[f][[2]]] == 4, AppendTo[t, n]], {n, 2, 100}]; t (* T. D. Noe, Mar 14 2014 *)

PARI

n=1;while(n<340,if(bigomega(fibonacci(n))==4,print1(n,", "));n++)

Extensions

More terms from Ryan Propper, May 22 2006