A222963 - OEIS

%I #30 Sep 08 2022 08:46:04

%S 0,4,10,28,40,70,88,130,208,238,340,418,460,550,700,868,928,1120,1258,

%T 1330,1558,1720,1978,2350,2548,2650,2860,2968,3190,4030,4288,4690,

%U 4828,5548,5698,6160,6640,6970,7480,8008,8188

%N a(n) = (p-3)*(p+3)/4 where p is the n-th prime.

%C Old name was: Numbers n such that sqrt(4*n+9) is prime.

%H Vincenzo Librandi, <a href="/A222963/b222963.txt">Table of n, a(n) for n = 2..1000</a>

%F 4*a(n)+9 = A001248(n).

%F a(n) = A166011(n)/2. - _Michel Marcus_, Apr 22 2016

%t Select[Range[0, 10000], PrimeQ[Sqrt[4 # + 9]]&]

%o (Magma) [(p^2-9)/4: p in PrimesInInterval(3, 200)];

%Y Subsequence of A028552.

%Y Cf. A000040, A001248, A005097, A168669.

%K nonn,easy

%O 2,2

%A _Vincenzo Librandi_, Apr 05 2013