A328932 Number of primes that are a concatenation of two positive integers whose sum is prime(n).

1, 0, 2, 2, 4, 3, 2, 6, 5, 9, 6, 7, 10, 11, 12, 14, 12, 16, 14, 17, 12, 15, 16, 20, 19, 19, 20, 17, 23, 23, 18, 27, 28, 24, 30, 25, 26, 26, 28, 30, 27, 30, 32, 27, 25, 27, 37, 42, 38, 32, 32, 33, 30, 39, 38, 36, 43, 38, 43, 42, 36, 36, 47, 47, 49, 38, 45, 48, 51, 50

Offset: 1

Author

Juri-Stepan Gerasimov, Oct 31 2019

Keywords

• nonn
• base
• easy

Examples

			a(3) = 2 because primes 23, 41 are concatenations of prime(3) = 5 = 2 + 3 = 4 + 1.
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A328903.

Cf. A000040, A066686, A067754.

Programs

Maple

a:= n-> (p-> add(`if`(isprime(parse(cat(i,
        p-i))), 1, 0), i=1..p-1))(ithprime(n)):
seq(a(n), n=1..80);  # Alois P. Heinz, Oct 31 2019

Formula

a(n) = A328903(A000040(n)).