A032617 Numbers k such that k concatenated with k+2 is a prime.

1, 7, 9, 27, 37, 45, 49, 51, 55, 61, 69, 75, 105, 109, 115, 117, 121, 151, 159, 181, 187, 195, 201, 211, 217, 225, 247, 271, 277, 285, 289, 291, 301, 309, 319, 321, 331, 337, 339, 357, 361, 367, 381, 391, 399, 405, 417, 421, 427, 429, 435, 439

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A032607.

Programs

Maple

filter:= n -> isprime(n*(10^(1+ilog10(n+2))+1)+2):
select(filter, [seq(i,i=1..1000,2)]); # Robert Israel, Nov 14 2019