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 A305818 Number of proper divisors d of n such that 2d+1 is a prime. 3
 0, 1, 1, 2, 1, 3, 1, 2, 2, 3, 1, 4, 1, 2, 3, 3, 1, 5, 1, 3, 2, 3, 1, 5, 2, 2, 3, 3, 1, 6, 1, 3, 3, 2, 2, 6, 1, 2, 2, 5, 1, 6, 1, 3, 5, 3, 1, 5, 1, 3, 2, 3, 1, 6, 3, 4, 2, 3, 1, 8, 1, 2, 4, 3, 2, 6, 1, 2, 3, 5, 1, 8, 1, 2, 4, 2, 2, 6, 1, 5, 3, 3, 1, 6, 2, 2, 3, 5, 1, 9, 1, 3, 2, 2, 2, 6, 1, 3, 5, 5, 1, 5, 1, 4, 6 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Number of terms of A005097 which are less than n that divide n. LINKS Antti Karttunen, Table of n, a(n) for n = 1..65537 FORMULA a(n) = Sum_{d|n, d

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Last modified January 25 19:09 EST 2020. Contains 331249 sequences. (Running on oeis4.)