A378122 a(n) = number of prime divisors of the sum of the first n primes.
1, 1, 2, 1, 2, 1, 2, 2, 2, 2, 2, 1, 3, 1, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 3, 2, 3, 2, 3, 2, 2, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 3, 3, 2, 4, 2, 2, 3, 4, 2, 2, 1, 3, 2, 3, 1, 2, 2, 3, 3, 3, 3, 3, 2, 3, 2, 2, 3, 4, 2, 3, 3, 2, 2, 2, 4, 3, 3
Offset: 1
Keywords
Examples
2+3+5+7+11 = 28 = 2*2*7, so a(5) = 2.
Programs
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Mathematica
a[n_] := PrimeNu[Total[Prime[Range[n]]]]; Array[a, 500]