login
A240679
Primes p such that p*10+k is prime for exactly two values of the digit k.
4
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
1,1
LINKS
EXAMPLE
2 is in the sequence because 23 and 29 are prime, but 21 and 27 are not prime.
MATHEMATICA
Select[Prime[Range[200]], Count[Table[10 #+k, {k, {1, 3, 7, 9}}], _?PrimeQ] == 2&] (* Harvey P. Dale, Jan 24 2019 *)
PROG
(PARI) forprime(p=2, 1500, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); if(t==2, print1(p, ", ")))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Colin Barker, Apr 10 2014
STATUS
approved