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
KEYWORD
base,nonn
AUTHOR
M. F. Hasler, Nov 25 2009
STATUS
approved