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A249381
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Prime numbers Q such that the concatenation Q,9,Q is prime.
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3
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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, 1069, 1091, 1151, 1171, 1213, 1249, 1259
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OFFSET
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1,1
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LINKS
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EXAMPLE
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393 is composite.
595 is composite.
797 is prime so a(1)=7.
11911 is composite.
13913 is prime so a(2)=13.
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MATHEMATICA
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Select[Prime[Range[200]], PrimeQ[FromDigits[Join[IntegerDigits[#], {9}, IntegerDigits[ #]]]]&] (* Harvey P. Dale, Jul 25 2015 *)
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PROG
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(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
(Python)
from sympy import isprime, primerange
def ok(p): swb = str(p); return isprime(int(swb + '9' + swb))
def aupto(lim): return [p for p in primerange(1, lim+1) if ok(p)]
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CROSSREFS
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Cf. similar sequences listed in A249374.
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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