%I #24 Sep 08 2022 08:45:40

%S 19,31,41,71,79,109,131,149,151,181,191,241,251,379,409,421,499,509,

%T 541,599,631,659,709,719,769,919,1009,1019,1021,1031,1109,1129,1151,

%U 1201,1231,1291,1399,1409,1451,1549,1601,1621,1721,1871,1931,2069,2131,2179

%N Primes p such that (p^2 + 4)/5 is prime.

%C The primes (p^2 + 4)/5 are 73, 193, 337, 1009, 1249, etc.

%C All terms == 1 or 9 (mod 10). - _Robert Israel_, Sep 16 2016

%H Vincenzo Librandi, <a href="/A154418/b154418.txt">Table of n, a(n) for n = 1..1000</a>

%p select(p -> isprime(p) and isprime((p^2+4)/5), [seq(seq(10*i+j,j=[1,9]),i=0..1000)]); # _Robert Israel_, Sep 16 2016

%t Select[Prime[Range[200]], PrimeQ[(#^2 + 4)/5] &] (* _Vincenzo Librandi_, Oct 15 2012 *)

%o (Magma) [p: p in PrimesInInterval(7, 2500) | IsPrime((p^2+4) div 5)]; // _Vincenzo Librandi_, Oct 15 2012

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Jan 09 2009, Dec 13 2010

%E Corrected and extended by _Zak Seidov_, Jan 13 2009