A127331 - OEIS

%I #7 Sep 08 2022 08:45:29

%S 2,5,11,29,31,61,71,101,109,199,229,241,269,331,379,431,491,631,691,

%T 821,919,941,991,1049,1061,1259,1289,1321,1409,1439,1451,1459,1571,

%U 1621,1831,1861,1931,2039,2089,2161,2251,2281,2311,2389,2399,2441,2539,2551

%N Primes p such that 6p-7 and 6p+7 are also primes.

%H Vincenzo Librandi, <a href="/A127331/b127331.txt">Table of n, a(n) for n = 1..1000</a>

%e 31, 6*31-7=179, 6*31+7=193 are all primes.

%t Select[Range[5000], PrimeQ[ # ] && PrimeQ[6# + 7] && PrimeQ[6# - 7] &]

%t Select[Prime[Range[3000]], PrimeQ[6 # - 7] && PrimeQ[6 # + 7]&] (* _Vincenzo Librandi_, Apr 09 2013 *)

%o (Magma) [p: p in PrimesUpTo(2600) | IsPrime(6*p-7) and IsPrime(6*p+7)]; // _Vincenzo Librandi_, Apr 09 2013

%K nonn,easy

%O 1,1

%A _Zerinvary Lajos_, Mar 30 2007