A023589 a(n) is the number of distinct prime divisors of 2*prime(n)+1.

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

Offset

1,4

Links

Michael De Vlieger, Table of n, a(n) for n = 1..10000

Mathematica

Array[PrimeNu[2 Prime[#] + 1] &, 99] (* Michael De Vlieger, Jul 09 2022 *)

Prog

(PARI) a(n) = omega(2*prime(n)+1) \\ Hugo Pfoertner, Jul 09 2022

Crossrefs

Cf. A001221, A072055.

Sequence in context: A154351 A112753 A281007 * A134034 A174886 A157415

Adjacent sequences: A023586 A023587 A023588 * A023590 A023591 A023592

Keyword

nonn

Author

Clark Kimberling

Status

approved