A023575 Number of distinct prime divisors of prime(n)+3.

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

Offset: 1

Author

Clark Kimberling

Keywords

• nonn
• easy

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000040 (prime), A001221 (omega).

Programs

Maple

f:= proc(p) nops(numtheory:-factorset(p+3)) end proc:
map(f, [seq(ithprime(i),i=1..100)]); # Robert Israel, Mar 06 2022

Mathematica

a[n_] := PrimeNu[Prime[n]+3]; Array[a, 100] (* Amiram Eldar, Sep 29 2024 *)

PARI

a(n) = omega(prime(n)+3); \\ Amiram Eldar, Sep 29 2024

Formula

a(n) = omega(prime(n)+3). - Wesley Ivan Hurt, Mar 06 2022