A032703 Numbers k such that k prefixed by '3' and followed by '1' is prime.

1, 3, 12, 18, 19, 22, 25, 27, 30, 33, 36, 37, 39, 46, 49, 51, 54, 57, 58, 63, 67, 69, 70, 76, 82, 85, 88, 91, 93, 105, 108, 109, 112, 115, 118, 123, 127, 132, 139, 148, 151, 153, 154, 160, 172, 174, 175, 177, 189, 198, 199, 205, 214, 219, 225, 226, 232, 234

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. A032702-A032733.

Programs

Maple

seq(op(select(x -> isprime(3*10^d+10*x+1),[$10^(d-2)..10^(d-1)-1])),d=2..4); # Robert Israel, Oct 22 2018

Mathematica

Select[Range[250],PrimeQ[FromDigits[Join[{3}, IntegerDigits[#], {1}]]]&]  (* Harvey P. Dale, Mar 28 2011 *)

Extensions

Offset changed to 1 by Robert Israel, Oct 22 2018