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

0,5

Comments

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

Links

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

Formula

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

Example

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), ...

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

Crossrefs

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

Sequence in context: A195910 A240590 A080769 * A143539 A249063 A362687

Adjacent sequences: A328900 A328901 A328902 * A328904 A328905 A328906

Keyword

nonn,base,look,easy

Author

Juri-Stepan Gerasimov, Oct 30 2019

Extensions

More terms from Alois P. Heinz, Oct 30 2019

Status

approved