A103802 Primes p such that 2p - 9 and 2p + 9 are both primes.

7, 11, 19, 31, 59, 61, 79, 101, 151, 179, 229, 311, 359, 389, 409, 521, 709, 719, 751, 809, 971, 1039, 1061, 1151, 1171, 1201, 1361, 1459, 1481, 1669, 1699, 1811, 1949, 1999, 2131, 2341, 2371, 2411, 2609, 2671, 2711, 2791, 2851, 3019, 3041, 3061, 3119

Offset: 1

Author

Zak Seidov, Feb 16 2005

Keywords

• nonn

Programs

Magma

[p: p in PrimesUpTo(3200)| IsPrime(2*p+9) and IsPrime(2*p-9) ]; // Vincenzo Librandi, Jan 28 2011

Mathematica

Select[Range[7,6000], PrimeQ[ # ] && PrimeQ[2# + 9] && PrimeQ[2# - 9] &]
okQ[n_]:=Module[{c=2n},PrimeQ[c+9]&&PrimeQ[c-9]]; Select[Prime[ Range[5,500]],okQ]  (* Harvey P. Dale, Apr 25 2011 *)

Formula

p, 2p-9 and 2p+9 all are positive and are primes (hence we omit p=2).