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A168163 Sophie Germain primes p such that the concatenation of p and 2p+1 is again prime. 1
3, 11, 23, 113, 173, 281, 359, 431, 491, 509, 719, 1103, 1229, 1559, 1889, 1931, 2039, 2393, 2459, 3413, 3539, 3761, 3911, 4391, 4793, 5303, 6113, 6263, 6329, 6491, 6563, 7643, 7823, 7883, 8069, 8093, 8951, 9221, 9473, 10061, 10091, 10589, 10781, 11369 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

A subsequence of A005384 (Sophie Germain primes: 2p+1 is prime) and of A168164 (which does not require 2p+1 to be prime).

The primes concat(p,2p+1) are listed in A168165.

LINKS

Table of n, a(n) for n=1..44.

PROG

(PARI) forprime(p=1, 19999, isprime(2*p+1) & isprime(eval(Str(p, 2*p+1))) & print1(p", "))

CROSSREFS

Sequence in context: A002515 A096297 A081857 * A120088 A081737 A005475

Adjacent sequences:  A168160 A168161 A168162 * A168164 A168165 A168166

KEYWORD

base,nonn

AUTHOR

M. F. Hasler, Nov 25 2009

STATUS

approved

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Last modified April 22 08:50 EDT 2019. Contains 322329 sequences. (Running on oeis4.)