A158708 Primes p such that p + floor(p/2) is prime.

2, 5, 13, 29, 41, 53, 73, 101, 109, 149, 181, 233, 281, 293, 349, 401, 409, 421, 449, 461, 541, 569, 613, 661, 673, 701, 709, 769, 809, 821, 853, 881, 953, 1021, 1033, 1109, 1129, 1193, 1201, 1249, 1289, 1301, 1409, 1429, 1453, 1481, 1493, 1669, 1693, 1789

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Mar 24 2009

Keywords

• nonn
• easy

Comments

Apart from the first term, primes of the form 4n+1 such that 6n+1 is also prime. [Charles R Greathouse IV, Nov 09 2011]

Links

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

Programs

Magma

[p: p in PrimesUpTo(1800) | IsPrime(p+ (p div 2))]; // Vincenzo Librandi, Apr 15 2013

Mathematica

lst={};Do[p=Prime[n];If[PrimeQ[Floor[p/2]+p],AppendTo[lst,p]],{n,6!}];lst
Select[Prime[Range[300]], PrimeQ[Floor[# / 2] + #]&] (* Vincenzo Librandi, Apr 15 2013 *)

PARI

forprime(p=2,1e4,if(isprime(p+p\2),print1(p", "))) \\ Charles R Greathouse IV, Nov 09 2011

PARI

print1(2);forprime(p=3,1e4,if(p%4==1&&isprime(p\4*6+1),print1(", "p))) \\ Charles R Greathouse IV, Nov 09 2011