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 A105221 a(n) is the sum of n's distinct prime factors below n. 11
 0, 0, 0, 2, 0, 5, 0, 2, 3, 7, 0, 5, 0, 9, 8, 2, 0, 5, 0, 7, 10, 13, 0, 5, 5, 15, 3, 9, 0, 10, 0, 2, 14, 19, 12, 5, 0, 21, 16, 7, 0, 12, 0, 13, 8, 25, 0, 5, 7, 7, 20, 15, 0, 5, 16, 9, 22, 31, 0, 10, 0, 33, 10, 2, 18, 16, 0, 19, 26, 14, 0, 5, 0, 39, 8, 21, 18, 18, 0, 7, 3, 43, 0, 12, 22, 45 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 LINKS T. D. Noe, Table of n, a(n) for n=1..1000 FORMULA a(n) = A008472(n) - A010051(n) * n. - Reinhard Zumkeller, Apr 05 2013 G.f.: Sum_{k>=1} prime(k) * x^(2*prime(k)) / (1 - x^prime(k)). - Ilya Gutkovskiy, Apr 13 2021 EXAMPLE a(12)=5 because 12's distinct prime factors 2 and 3 sum to 5. MATHEMATICA Table[Total@Select[Join@@Union@*Table@@@FactorInteger@k, #

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Last modified November 30 00:02 EST 2022. Contains 358431 sequences. (Running on oeis4.)