A249375 Prime numbers Q such that the concatenation Q,2,Q is prime.

7, 19, 31, 61, 79, 193, 283, 367, 373, 421, 499, 547, 619, 733, 751, 883, 997, 1021, 1033, 1039, 1069, 1153, 1171, 1279, 1399, 1483, 1543, 1567, 1753, 1831, 1879, 1951, 1999, 2083, 2161, 2179, 2251, 2281, 2287, 2503, 2671, 2707, 2713, 2767, 2797, 2953, 3019

Offset

1,1

Links

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

Example

323 is composite, 525 is composite, 727 is prime so a(1)=7.

Maple

q:= n-> isprime(parse(cat(n, 2, n))):
select(q, [ithprime(i)$i=1..500])[];  # Alois P. Heinz, Jun 17 2021

Mathematica

cq2Q[n_]:=Module[{idn=IntegerDigits[n]}, PrimeQ[FromDigits[Join[idn, {2}, idn]]]]; Select[Prime[Range[400]], cq2Q] (* Harvey P. Dale, Apr 17 2019 *)

Prog

(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 2), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [2] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014
(Python)
from sympy import isprime, primerange
def ok(p): s = str(p); return isprime(int(s+'2'+s))
print(list(filter(ok, primerange(1, 3020)))) # Michael S. Branicky, Jul 19 2021

Crossrefs

Cf. similar sequences listed in A249374.

Sequence in context: A298019 A169605 A216532 * A212492 A374535 A234310

Adjacent sequences: A249372 A249373 A249374 * A249376 A249377 A249378

Keyword

nonn,base

Author

Pierre CAMI, Oct 27 2014

Status

approved