A032624 Numbers k such that k concatenated with k+9 is a prime.

2, 10, 14, 20, 28, 38, 40, 50, 52, 58, 62, 64, 70, 80, 82, 100, 104, 110, 112, 118, 122, 124, 142, 148, 160, 164, 170, 172, 178, 188, 194, 208, 218, 224, 230, 238, 244, 248, 250, 260, 262, 274, 284, 292, 298, 308, 320, 338, 344, 352, 362, 364, 382, 398, 400

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. A032614.

Programs

Maple

tcat:= (a,b) -> a*10^(1+ilog10(b))+b:
select(t -> isprime(tcat(t,t+9)), [seq(i,i=2..1000,2)]); # Robert Israel, Sep 04 2024

Mathematica

Select[Range[400],PrimeQ[FromDigits[Join[IntegerDigits[#],IntegerDigits[#+9]]]]&] (* Stefano Spezia, Sep 04 2023 *)