A032725 Numbers k such that k prefixed by '9' and followed by '7' is prime.

0, 3, 4, 6, 7, 9, 12, 13, 15, 18, 22, 25, 27, 33, 37, 39, 43, 46, 49, 54, 58, 67, 69, 76, 78, 81, 85, 88, 90, 96, 109, 112, 123, 129, 136, 138, 139, 145, 157, 175, 180, 183, 186, 195, 196, 199, 207, 210, 217, 222, 223, 229, 231, 234, 235, 237, 238, 246, 250, 255

Offset: 1

Author

Patrick De Geest, May 15 1998

Keywords

• nonn
• base

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A032702-A032733.

Programs

Mathematica

Select[Range[0,300],PrimeQ[FromDigits[Join[{9},IntegerDigits[#],{7}]]]&] (* Harvey P. Dale, Mar 01 2025 *)

Extensions

Offset changed by Andrew Howroyd, Aug 13 2024