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A249381 Prime numbers Q such that the concatenation Q,9,Q is prime. 3
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 (list; graph; refs; listen; history; text; internal format)
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

(PFGW & SCRIPT), the pre10.txt file with the 10000000 first 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)+9*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), 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

CROSSREFS

Cf. similar sequences listed in A249374.

Sequence in context: A110074 A058383 A005471 * A040096 A181938 A073648

Adjacent sequences:  A249378 A249379 A249380 * A249382 A249383 A249384

KEYWORD

nonn,base

AUTHOR

Pierre CAMI, Oct 27 2014

STATUS

approved

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Last modified April 17 08:40 EDT 2021. Contains 343064 sequences. (Running on oeis4.)