A249381 Prime numbers Q such that the concatenation Q,9,Q is prime.

7, 13, 19, 41, 43, 47, 61, 67, 71, 73, 79, 83, 89, 107, 137, 149, 173, 179, 211, 229, 269, 277, 281, 283, 379, 401, 431, 443, 491, 523, 547, 557, 577, 599, 607, 613, 619, 647, 683, 691, 823, 863, 877, 919, 977, 1031, 1069, 1091, 1151, 1171, 1213, 1249, 1259

Offset

1,1

Links

Pierre CAMI, Table of n, a(n) for n = 1..10000

Example

393 is composite.
595 is composite.
797 is prime so a(1)=7.
11911 is composite.
13913 is prime so a(2)=13.

Mathematica

Select[Prime[Range[200]], PrimeQ[FromDigits[Join[IntegerDigits[#], {9}, IntegerDigits[ #]]]]&] (* Harvey P. Dale, Jul 25 2015 *)

Prog

(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 9), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [9] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014
(Python)
from sympy import isprime, primerange
def ok(p): swb = str(p); return isprime(int(swb + '9' + swb))
def aupto(lim): return [p for p in primerange(1, lim+1) if ok(p)]
print(aupto(1260)) # Michael S. Branicky, Jul 13 2021

Crossrefs

Cf. similar sequences listed in A249374.

Sequence in context: A110074 A058383 A005471 * A040096 A358322 A181938

Adjacent sequences: A249378 A249379 A249380 * A249382 A249383 A249384

Keyword

nonn,base

Author

Pierre CAMI, Oct 27 2014

Status

approved