A351613 Number of pairs of divisors of n, (d1,d2) d1<=d2, such that d1+d2 is prime.

1, 2, 1, 3, 1, 4, 1, 3, 1, 4, 1, 7, 1, 2, 1, 4, 1, 6, 1, 5, 1, 4, 1, 8, 1, 2, 1, 5, 1, 10, 1, 4, 1, 3, 1, 11, 1, 2, 1, 7, 1, 8, 1, 5, 1, 3, 1, 10, 1, 4, 1, 5, 1, 7, 1, 5, 1, 4, 1, 17, 1, 2, 1, 4, 1, 8, 1, 4, 1, 8, 1, 14, 1, 2, 1, 4, 1, 8, 1, 8, 1, 4, 1, 15, 1, 2, 1, 7, 1, 15

Offset

1,2

Links

Table of n, a(n) for n=1..90.

Formula

a(n) = Sum_{d1|n, d2|n, d1<=d2} c(d1 + d2), where c is the prime characteristic (A010051).

Example

a(12) = 7; The pairs are (1,1), (1,2), (1,4), (1,6), (1,12), (2,3), (3,4).

Crossrefs

Cf. A010051.

Sequence in context: A366421 A218533 A328578 * A094741 A360653 A285577

Adjacent sequences: A351610 A351611 A351612 * A351614 A351615 A351616

Keyword

nonn

Author

Wesley Ivan Hurt, Feb 14 2022

Status

approved