A249378 Prime numbers Q such that the concatenation Q,5,Q is prime.

3, 7, 13, 31, 37, 43, 61, 67, 79, 163, 277, 313, 331, 433, 439, 487, 523, 541, 607, 619, 643, 733, 769, 907, 937, 991, 1033, 1051, 1213, 1291, 1303, 1321, 1381, 1423, 1459, 1489, 1597, 1699, 1741, 1759, 1831, 1867

Offset

1,1

Links

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

Example

353 is prime so a(1)=3.
555 is composite, 757 is prime, so a(2)=7.

Mathematica

q5Q[n_]:=PrimeQ[FromDigits[Join[IntegerDigits[n], {5}, IntegerDigits[n]]]]; Select[Prime[Range[300]], q5Q] (* Harvey P. Dale, Jul 21 2020 *)

Prog

(PFGW & SCRIPT), the pre10.txt file with the first 10000000 prime numbers.
SCRIPT
DIM i, 0
DIM j
DIM k
DIM n, 1
OPENFILEOUT myf, a(n).txt
OPENFILEIN maf, pre10.txt
GETNEXT j, maf
LABEL loop1
GETNEXT j, maf
IF j>10^n THEN SET n, n+1
SET k, j*10^(n+1)+5*10^n+j
PRP k
IF ISPRP THEN GOTO w
GOTO loop1
LABEL w
SET i, i+1
WRITE myf, j
IF i>9999 THEN END
GOTO loop1
(PARI) lista(nn) = {forprime(p=1, nn, if (isprime(eval(concat(concat(Str(p), 5), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [5] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014

Crossrefs

Cf. similar sequences listed in A249374.

Sequence in context: A199218 A062700 A330835 * A136060 A023227 A031157

Adjacent sequences: A249375 A249376 A249377 * A249379 A249380 A249381

Keyword

nonn

Author

Pierre CAMI, Oct 27 2014

Status

approved