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A114841
Indices of Fibonacci numbers with 3 distinct prime factors.
13
15, 16, 18, 21, 33, 35, 37, 38, 39, 46, 49, 51, 58, 62, 65, 67, 82, 86, 103, 106, 119, 122, 125, 139, 142, 145, 158, 166, 179, 181, 226, 233, 235, 241, 257, 263, 274, 281, 299, 301, 317, 337, 383, 389, 419, 457, 463, 473, 479, 491, 521, 541, 557, 619, 643, 659, 706, 719, 739, 751, 857, 863, 877, 881, 883, 911, 947, 983, 1021, 1033, 1061, 1069, 1109, 1117, 1123, 1181, 1187, 1193, 1213, 1226
OFFSET
1,1
EXAMPLE
a(1) = 15 because 15th Fibonacci number has 3 distinct prime factors (i.e., 610 = 2 * 5 * 61).
MAPLE
with(numtheory): with(combinat):
a:=n->`if`(nops(factorset(fibonacci(n)))=3, n, NULL); [seq(a(n), n=1..300)]; # Muniru A Asiru, Mar 25 2018
MATHEMATICA
Select[Range[500], PrimeNu[Fibonacci[#]]==3 &] (* Vincenzo Librandi, Mar 26 2018 *)
PROG
(PARI) n=1; while(n<340, if(omega(fibonacci(n))==3, print1(n, ", ")); n++)
(Magma) [n: n in [1..350] |(#(PrimeDivisors(Fibonacci(n)))) eq 3]; // Vincenzo Librandi, Mar 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Shyam Sunder Gupta, Feb 19 2006
EXTENSIONS
More terms from Ryan Propper, Apr 26 2006
a(57)-a(80) from Max Alekseyev, Aug 18 2013
STATUS
approved