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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
OFFSET
1,4
COMMENTS
Number of terms of A005097 which are less than n that divide n.
LINKS
FORMULA
a(n) = Sum_{d|n, d<n} A101264(d).
a(n) = A086668(n) - A101264(n).
PROG
(PARI) A305818(n) = sumdiv(n, d, (d<n)*isprime(d+d+1));
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Jun 15 2018
STATUS
approved