A289994 a(1) = 1, a(2) = 2, a(n) = smallest number not occurring earlier such that the concatenation a(n-2), a(n-1) and a(n) is a prime.

1, 2, 7, 11, 19, 13, 9, 21, 43, 3, 31, 49, 17, 37, 29, 41, 27, 39, 67, 33, 81, 53, 51, 23, 89, 91, 59, 47, 73, 61, 87, 99, 79, 63, 117, 113, 77, 127, 103, 93, 111, 71, 69, 101, 147, 57, 97, 133, 119, 121, 139, 131, 107, 157, 151, 123, 153, 83, 143, 169, 109, 137

Offset: 1

Author

Seiichi Manyama, Sep 02 2017

Keywords

• nonn
• base

Examples

			127, 2711, 71119, 111913, ... are primes.
		

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A075607, A073676, A083754, A110772.