A240679 Primes p such that p*10+k is prime for exactly two values of the digit k.

2, 3, 5, 17, 23, 37, 59, 67, 73, 97, 101, 127, 149, 157, 193, 197, 211, 223, 229, 233, 239, 241, 269, 283, 331, 337, 349, 353, 373, 379, 401, 433, 439, 463, 467, 479, 487, 499, 571, 607, 613, 619, 631, 673, 691, 701, 733, 757, 769, 811, 853, 859, 937, 941

Offset: 1

Author

Colin Barker, Apr 10 2014

Keywords

• nonn
• base

Examples

			2 is in the sequence because 23 and 29 are prime, but 21 and 27 are not prime.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A067267, A119289, A240678, A240680, A240689.

Programs

Mathematica

Select[Prime[Range[200]],Count[Table[10 #+k,{k,{1,3,7,9}}],?PrimeQ] == 2&] (* _Harvey P. Dale, Jan 24 2019 *)

PARI

forprime(p=2, 1500, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); if(t==2, print1(p, ", ")))