A032721 Numbers k such that k prefixed by '4' and followed by '7' is prime.

5, 6, 8, 12, 15, 17, 21, 29, 32, 33, 35, 39, 44, 45, 50, 51, 54, 56, 59, 63, 65, 78, 81, 87, 93, 95, 96, 98, 101, 104, 105, 107, 111, 117, 122, 125, 135, 138, 146, 150, 159, 161, 162, 164, 168, 173, 177, 188, 189, 192, 194, 195, 201, 215, 218, 219, 222, 225

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[300],PrimeQ[FromDigits[Join[{4},IntegerDigits[#],{7}]]]&] (* Harvey P. Dale, Jan 08 2019 *)

Extensions

Offset changed by Andrew Howroyd, Aug 13 2024