A378123 a(n) = number of prime divisors of the sum of the first n odd primes.

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

Offset: 1

Author

Clark Kimberling, Nov 17 2024

Keywords

• nonn

Examples

			3+5+7+11+13 = 39 = 3*13, so a(5) = 2.
		

Crossrefs

Cf. A000040, A071215, A008334, A008335, A378122.

Cf. A001221, A071148.

Programs

Mathematica

a[n_] := PrimeNu[Total[Prime[1+Range[n]]]]; Array[a, 500]

PARI

a378123(n)=omega(sum(k=2,n+1,prime(k))) \\ Hugo Pfoertner, Nov 19 2024

Formula

a(n) = A001221(A071148(n)).