A032621 Numbers k such that k concatenated with k+6 is a prime.

1, 11, 13, 17, 25, 31, 35, 43, 65, 71, 83, 95, 97, 101, 125, 127, 137, 151, 155, 157, 161, 163, 167, 187, 197, 203, 205, 211, 217, 221, 223, 227, 233, 235, 245, 251, 257, 263, 265, 271, 283, 317, 331, 335, 337, 341, 353, 355, 373, 385, 391, 401, 427, 433

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. A032611.

Programs

Maple

filter:= n -> isprime(n * 10^(1+ilog10(n+6)) + n + 6):
select(filter, [seq(i,i=1..1000,2)]); # Robert Israel, May 13 2025

Mathematica

Select[Range[1,501,2],PrimeQ[FromDigits[Join[IntegerDigits[#], IntegerDigits[ #+6]]]]&] (* Harvey P. Dale, Nov 17 2013 *)