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URL: https://oeis.org/A378123

⇱ A378123 - OEIS

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A378123
a(n) = number of prime divisors of the sum of the first n odd primes.
2
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
1,3
FORMULA
a(n) = A001221(A071148(n)).
EXAMPLE
3+5+7+11+13 = 39 = 3*13, so a(5) = 2.
MATHEMATICA
a[n_] := PrimeNu[Total[Prime[1+Range[n]]]]; Array[a, 500]
PROG
(PARI) a378123(n)=omega(sum(k=2, n+1, prime(k))) \\ Hugo Pfoertner, Nov 19 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Nov 17 2024
STATUS
approved