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A344931 Sum of the distinct even-indexed prime divisors, p_{2k}, of n. 3
0, 0, 3, 0, 0, 3, 7, 0, 3, 0, 0, 3, 13, 7, 3, 0, 0, 3, 19, 0, 10, 0, 0, 3, 0, 13, 3, 7, 29, 3, 0, 0, 3, 0, 7, 3, 37, 19, 16, 0, 0, 10, 43, 0, 3, 0, 0, 3, 7, 0, 3, 13, 53, 3, 0, 7, 22, 29, 0, 3, 61, 0, 10, 0, 13, 3, 0, 0, 3, 7, 71, 3, 0, 37, 3, 19, 7, 16, 79, 0, 3, 0, 0, 10, 0, 43, 32 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
a(n) = Sum_{p|n} p * ((pi(p)+1) mod 2 ).
G.f.: Sum_{k>=1} prime(2*k) * x^prime(2*k) / (1 - x^prime(2*k)). - Ilya Gutkovskiy, Oct 24 2023
EXAMPLE
a(12) = Sum_{p|12} p * ((pi(p)+1) mod 2 ) = 2*0 + 3*1 = 3.
MATHEMATICA
Table[Sum[k*Mod[PrimePi[k] + 1, 2] (PrimePi[k] - PrimePi[k - 1]) (1 - Ceiling[n/k] + Floor[n/k]), {k, n}], {n, 100}]
PROG
(PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, if (!(primepi(f[k, 1]) % 2), f[k, 1])); \\ Michel Marcus, Jun 12 2021
CROSSREFS
Cf. A000720 (pi), A008472 (sopf), A005074, A324966.
Cf. A344908 (sum of distinct odd-indexed prime divisors).
Sequence in context: A318925 A285213 A285339 * A005082 A050452 A267875
KEYWORD
nonn
AUTHOR
Wesley Ivan Hurt, Jun 02 2021
STATUS
approved

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Last modified March 28 08:22 EDT 2024. Contains 371236 sequences. (Running on oeis4.)