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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.)