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A337531 Number of ways that the divisors of 2n can be written as unordered sums of two other prime divisors of 2n (not necessarily distinct). 0
0, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 3, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 4, 1, 1, 2, 2, 3, 2, 1, 2, 2, 2, 1, 3, 1, 2, 3, 2, 1, 2, 1, 2, 2, 2, 1, 2, 2, 2, 2, 2, 1, 5, 1, 2, 3, 1, 2, 3, 1, 2, 2, 4, 1, 2, 1, 2, 3, 2, 2, 3, 1, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 4, 2, 2, 2, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..96.

FORMULA

a(n) = Sum_{d1|(2*n), d2|(2*n), d3|(2*n), d1,d2 prime} [d1 + d2 = d3], where [ ] is the Iverson bracket.

EXAMPLE

a(15) = 3; The divisors of 2*15 = 30 are {1,2,3,5,6,10,15,30} and since 2 + 3 = 5, 3 + 3 = 6 and 5 + 5 = 10, a(15) = 3.

CROSSREFS

Cf. A175393.

Sequence in context: A036475 A330746 A316555 * A316556 A187279 A076820

Adjacent sequences: A337528 A337529 A337530 * A337532 A337533 A337534

KEYWORD

nonn

AUTHOR

Wesley Ivan Hurt, Aug 30 2020

STATUS

approved

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Last modified January 31 20:46 EST 2023. Contains 359981 sequences. (Running on oeis4.)