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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<n} A101264(d).

a(n) = A086668(n) - A101264(n).

PROG

(PARI) A305818(n) = sumdiv(n, d, (d<n)*isprime(d+d+1));

CROSSREFS

Cf. A005097, A086668, A101264.

Sequence in context: A154263 A293435 A294901 * A303757 A323014 A182850

Adjacent sequences:  A305815 A305816 A305817 * A305819 A305820 A305821

KEYWORD

nonn

AUTHOR

Antti Karttunen, Jun 15 2018

STATUS

approved

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