A067390 Number of distinct prime factors in 2^n + 3.

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

Offset: 1

Author

Benoit Cloitre, Feb 23 2002

Keywords

• nonn

Examples

			a(5) = 2 since 2^5 + 3 = 35 = 5 * 7 has 2 distinct prime factors.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..699

Crossrefs

Cf. A001221, A062709.

Programs

Magma

[#PrimeDivisors(2^n+3):n in [1..100]]; // Marius A. Burtea, Feb 06 2020

Mathematica

PrimeNu @ Table[2^n + 3, {n, 1, 50}] (* Amiram Eldar, Feb 06 2020 *)

Formula

a(n) = A001221(A062709(n)). - Amiram Eldar, Feb 06 2020