A240680 Primes p such that p*10+k is prime for exactly three values of the digit k.

7, 13, 31, 43, 61, 103, 109, 199, 271, 367, 409, 421, 523, 541, 547, 787, 823, 829, 883, 1009, 1033, 1117, 1237, 1291, 1669, 1999, 2131, 2161, 2203, 2269, 2437, 2503, 2593, 2671, 2857, 3049, 3253, 3271, 3361, 3559, 3583, 3769, 3823, 4003, 4201, 4339, 4357

Offset

1,1

Links

Bruno Berselli, Table of n, a(n) for n = 1..1000

Example

7 is in the sequence because 71, 73 and 79 are prime, but 77 is not prime.

Mathematica

Select[Prime[Range[600]], Total[Boole[PrimeQ[10#+{1, 3, 7, 9}]]]==3&] (* Harvey P. Dale, Apr 07 2023 *)

Prog

(PARI) forprime(p=2, 10000, t=0; forstep(k=1, 9, 2, if(isprime(p*10+k), t++)); if(t==3, print1(p, ", ")))
(Magma) [p: p in PrimesUpTo(10^4) | {k: k in [1, 3, 7, 9] | IsPrime(p*10+k)} in Subsets({1, 3, 7, 9}, 3)]; // Bruno Berselli, Apr 10 2014

Crossrefs

Cf. A067267, A119289, A240678, A240679, A240689.

Sequence in context: A231626 A343302 A110912 * A308851 A298027 A085104

Adjacent sequences: A240677 A240678 A240679 * A240681 A240682 A240683

Keyword

nonn,base

Author

Colin Barker, Apr 10 2014

Status

approved