

A168164


Primes p such that the concatenation of p and 2p+1 is again prime.


4



3, 11, 13, 23, 31, 59, 71, 79, 101, 113, 151, 163, 173, 193, 199, 229, 269, 281, 331, 359, 383, 431, 491, 509, 569, 661, 709, 719, 829, 839, 853, 929, 991, 1061, 1103, 1193, 1229, 1231, 1249, 1259, 1321, 1559, 1571, 1699, 1759, 1873, 1889, 1931, 1949, 1993
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OFFSET

1,1


COMMENTS

The primes concat(p,2p+1) are listed in A168166.


LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000


MATHEMATICA

p2pQ[n_]:=PrimeQ[FromDigits[IntegerDigits/@Join[n, 2n+1]]]; Select[ Prime[ Range[ 400]], p2pQ] (* Harvey P. Dale, May 03 2014 *)


PROG

(PARI) forprime(p=1, 1999, isprime(eval(Str(p, 2*p+1))) & print1(p", "))


CROSSREFS

Sequence in context: A281816 A117682 A045429 * A296933 A270543 A213697
Adjacent sequences: A168161 A168162 A168163 * A168165 A168166 A168167


KEYWORD

base,nonn


AUTHOR

M. F. Hasler, Nov 25 2009


STATUS

approved



