A023568 Number of distinct prime divisors of prime(n)-3.

0, 0, 1, 1, 1, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1, 2, 3, 2, 2, 2, 2, 2, 2, 2, 2, 3, 2, 1, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 2, 3, 2, 2, 3, 3, 2, 2, 2, 3, 3, 2, 3, 3, 2, 2, 2, 2, 2, 3, 2, 3, 3, 2, 3, 2, 2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 2, 2, 3, 2, 3, 2, 2, 2, 2, 3, 3, 3

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

a(n) = 1 if prime(n) is in A057733. - Robert Israel, Dec 28 2015

Links

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

Crossrefs

Cf. A023569, A057733.

Programs

Maple

0,0,seq(nops(numtheory:-factorset(ithprime(i)-3)), i=3..100); # Robert Israel, Dec 28 2015

Mathematica

Join[{0,0},PrimeNu/@(Prime[Range[3,100]]-3)] (* Harvey P. Dale, Sep 09 2017 *)