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A249380
Prime numbers Q such that the concatenation Q,8,Q is prime.
3
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
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
KEYWORD
nonn,base
AUTHOR
Pierre CAMI, Oct 27 2014
STATUS
approved