A328903 Number of primes that are a concatenation of two positive integers whose sum is n.

0, 0, 1, 0, 2, 2, 0, 2, 3, 0, 3, 4, 0, 3, 5, 0, 4, 2, 0, 6, 5, 0, 4, 5, 0, 6, 7, 0, 6, 9, 0, 6, 8, 0, 9, 8, 0, 7, 7, 0, 9, 10, 0, 11, 2, 0, 12, 12, 0, 10, 11, 0, 11, 14, 0, 3, 10, 0, 10, 12, 0, 16, 12, 0, 16, 14, 0, 14, 19, 0, 13, 17, 0, 12, 16, 0, 15, 2, 0

Offset: 0

Author

Juri-Stepan Gerasimov, Oct 30 2019

Keywords

• nonn
• base
• look
• easy

Comments

First n > 1 with n != 0 (mod 3) and a(n) = 0 is n = 4477. - Alois P. Heinz, Oct 30 2019

Examples

			1(-), 2(11), 3(-), 4(13, 31), 5(23, 41), 6(-), 7(43, 61), 8(17, 53, 71), 9(-), 10(19, 37, 73), 11(29, 47, 83, 101), 12(-), 13(67, 103, 211), ...
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..20000

Crossrefs

Cf. A000040, A008486, A008585, A066686, A067574, A154530, A328932.

Programs

Maple

a:= proc(n) option remember; `if`(irem(n, 3)=0, 0, add(
     `if`(isprime(parse(cat(i, n-i))), 1, 0), i=1..n-1))
    end:
seq(a(n), n=0..100);  # Alois P. Heinz, Oct 30 2019

Formula

a(n) = 0 if n = 1 or n == 0 (mod 3). - Alois P. Heinz, Oct 30 2019

Extensions

More terms from Alois P. Heinz, Oct 30 2019