A249380 Prime numbers Q such that the concatenation Q,8,Q is prime.

3, 7, 19, 61, 67, 109, 139, 277, 337, 349, 523, 547, 727, 751, 823, 853, 859, 883, 991, 1009, 1063, 1093, 1231, 1237, 1279, 1291, 1321, 1423, 1429, 1447, 1531, 1609, 1657, 1723, 1759, 1867, 1933, 1951, 2089, 2113, 2131, 2683

Offset

1,1

Links

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

Example

383 is prime so a(1)=3.
585 is composite, 787 is prime so a(2)=7.

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)+8*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), 8), Str(p)))), print1(p, ", ")); ); } \\ Michel Marcus, Oct 27 2014
(Magma) [p: p in PrimesUpTo(3000) | IsPrime(Seqint(Intseq(p) cat [8] cat Intseq(p)))]; // Vincenzo Librandi, Oct 27 2014

Crossrefs

Cf. similar sequences listed in A249374.

Sequence in context: A148667 A148668 A148669 * A364626 A210985 A160128

Adjacent sequences: A249377 A249378 A249379 * A249381 A249382 A249383

Keyword

nonn,base

Author

Pierre CAMI, Oct 27 2014

Status

approved