A089531 Primes p such that (p-3)/2 is also prime.

7, 13, 17, 29, 37, 41, 61, 89, 97, 109, 137, 149, 181, 197, 229, 257, 277, 281, 317, 337, 349, 389, 397, 401, 449, 457, 461, 541, 557, 569, 617, 677, 701, 709, 761, 769, 797, 821, 881, 929, 937, 977, 1009, 1021, 1049, 1097, 1117, 1129, 1201, 1217, 1229, 1237

Offset: 1

Author

Ray Chandler, Nov 07 2003

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A023204, A089530, A089532.

Programs

Magma

[p: p in PrimesUpTo(1300) | IsPrime((p-3) div 2)]; // Vincenzo Librandi, Apr 13 2013

Mathematica

Clear[lst,n,f] f[n_]:=PrimeQ[(n-3)/2]; lst={};Do[p=Prime[n];If[f[p],AppendTo[lst,p]],{n,6!}];lst (* Vladimir Joseph Stephan Orlovsky, Oct 13 2009 *)
Select[Prime[Range[300]], PrimeQ[(# - 3) / 2]&] (* Vincenzo Librandi, Apr 13 2013 *)

PARI

is(n)=isprime(n) && isprime((n-3)\2) \\ Charles R Greathouse IV, Sep 09 2014

Formula

a(n) = 2*A023204(n) + 3.

Extensions

Comment from Juri-Stepan Gerasimov used as new name (old name moved to formulas). - Charles R Greathouse IV, Sep 09 2014