A168164 Primes p such that the concatenation of p and 2p+1 is again prime.

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

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