%I #9 Sep 08 2022 08:45:47

%S 7,11,13,19,23,29,41,43,59,73,79,103,109,113,131,139,173,181,191,233,

%T 263,271,283,293,311,313,331,379,389,401,409,421,433,439,443,463,491,

%U 499,521,599,613,631,641,673,701,719,751,773,839,859,929,953,983,991,1033,1039,1063

%N Primes p such that (p^2-1)/4-p is also prime.

%H Vincenzo Librandi, <a href="/A165349/b165349.txt">Table of n, a(n) for n = 1..1000</a>

%F A165557(n) = (a(n)^2-1)/4-a(n).

%e For p=7, (p^2-1)/4-p=5, which is prime. For p=11, (p^2-1)/4-p=19, which is prime. p=13: (p^2-1)/4-p=29.

%t Select[Prime[Range[180]], PrimeQ[(#^2 - 1) / 4 - #]&] (* _Vincenzo Librandi_, Apr 10 2013 *)

%o (Magma) [p: p in PrimesInInterval(5, 1200) | IsPrime(((p^2-1) div 4) - p)]; // _Vincenzo Librandi_, Apr 10 2013

%Y Cf. A165557.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Sep 22 2009

%E Extended by _R. J. Mathar_, Sep 26 2009