A158708 - OEIS

%I #18 Sep 08 2022 08:45:43

%S 2,5,13,29,41,53,73,101,109,149,181,233,281,293,349,401,409,421,449,

%T 461,541,569,613,661,673,701,709,769,809,821,853,881,953,1021,1033,

%U 1109,1129,1193,1201,1249,1289,1301,1409,1429,1453,1481,1493,1669,1693,1789

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

%C 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]

%H Vincenzo Librandi, <a href="/A158708/b158708.txt">Table of n, a(n) for n = 1..1000</a>

%t lst={};Do[p=Prime[n];If[PrimeQ[Floor[p/2]+p],AppendTo[lst,p]],{n,6!}];lst

%t Select[Prime[Range[300]], PrimeQ[Floor[# / 2] + #]&] (* _Vincenzo Librandi_, Apr 15 2013 *)

%o (PARI) forprime(p=2,1e4,if(isprime(p+p\2),print1(p", "))) \\ _Charles R Greathouse IV_, Nov 09 2011

%o (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

%o (Magma) [p: p in PrimesUpTo(1800) | IsPrime(p+ (p div 2))]; // _Vincenzo Librandi_, Apr 15 2013

%K nonn,easy

%O 1,1

%A _Vladimir Joseph Stephan Orlovsky_, Mar 24 2009