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A249378 Prime numbers Q such that the concatenation Q,5,Q is prime. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 18 08:18 EDT 2021. Contains 348066 sequences. (Running on oeis4.)