A023582 Number of distinct prime divisors of 2*prime(n)-1.

1, 1, 1, 1, 2, 1, 2, 1, 2, 2, 1, 1, 1, 2, 2, 3, 2, 1, 2, 2, 2, 1, 3, 2, 1, 2, 2, 2, 2, 2, 2, 2, 3, 1, 2, 2, 1, 2, 2, 3, 3, 1, 2, 3, 2, 1, 1, 2, 2, 1, 3, 2, 2, 2, 2, 3, 2, 1, 2, 3, 2, 3, 1, 2, 1, 2, 1, 1, 3, 2, 3, 2, 1, 2, 1, 3, 3, 2, 2, 2, 2, 1, 3, 2, 1, 3, 3, 2, 2, 2, 2, 3, 2, 2, 1, 3, 2, 2, 3

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..5000

Programs

Maple

seq(nops(numtheory:-factorset(2*ithprime(n)-1)),n=1..120); # Muniru A Asiru, Apr 29 2019

Mathematica

PrimeNu[2*Prime[Range[100]]-1] (* Harvey P. Dale, Jan 25 2015 *)

PARI

a(n) = omega(2*prime(n)-1); \\ Michel Marcus, Oct 01 2013

Formula

a(n) = A001221(A076274(n)). - Michel Marcus, Oct 01 2013