A032664 Digit '1' concatenated with a(n) is a prime.

1, 3, 7, 9, 13, 27, 31, 37, 39, 49, 51, 57, 63, 67, 73, 79, 81, 91, 93, 97, 99, 103, 109, 117, 123, 129, 151, 153, 163, 171, 181, 187, 193, 201, 213, 217, 223, 229, 231, 237, 249, 259, 277, 279, 283, 289, 291, 297, 301, 303, 307, 319, 321, 327, 361, 367, 373

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Programs

Mathematica

Select[Range[400],PrimeQ[10^IntegerLength[#]+#]&] (* Harvey P. Dale, Dec 16 2019 *)

Extensions

Edited by Charles R Greathouse IV, Apr 24 2010