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

1,1

Links

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

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

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

Sequence in context: A049577 A353153 A121558 * A180474 A155978 A235925

Adjacent sequences: A240676 A240677 A240678 * A240680 A240681 A240682

Keyword

nonn,base

Author

Colin Barker, Apr 10 2014

Status

approved