A023524 Number of distinct prime divisors of prime(n)*prime(n-1) + 1.

1, 1, 1, 2, 3, 2, 3, 2, 3, 2, 3, 3, 4, 3, 3, 3, 3, 3, 3, 4, 2, 3, 3, 2, 3, 4, 3, 4, 2, 3, 4, 4, 3, 3, 3, 3, 2, 3, 4, 3, 3, 3, 4, 2, 3, 3, 5, 3, 5, 3, 3, 2, 3, 3, 2, 4, 3, 3, 3, 3, 3, 4, 3, 3, 3, 4, 3, 3, 4, 3, 3, 4, 4, 3, 3, 4, 4, 4, 4, 6, 3, 4, 3, 2, 2, 3, 2

Offset: 1

Author

Clark Kimberling

Keywords

• nonn

Comments

This is taking prime(0)=1. - Robert Israel, Dec 22 2015

Links

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

Programs

Magma

[#PrimeDivisors((NthPrime(n)*(NthPrime(n-1))+1)): n in [1..100]]; // Vincenzo Librandi, Dec 23 2015

Maple

1,seq(nops(numtheory:-factorset(ithprime(n)*ithprime(n-1)+1)), n=2..100); # Robert Israel, Dec 22 2015

Mathematica

Prepend[Table[PrimeNu[Prime@ n Prime[n - 1] + 1], {n, 2, 80}], 1] (* Michael De Vlieger, Dec 22 2015 *)

PARI

a(n) = if (n==1, 1, omega(prime(n)*prime(n-1) + 1)); \\ Michel Marcus, Dec 22 2015