A242331 - OEIS

%I #12 Sep 08 2022 08:46:08

%S 1,6,16,18,20,24,26,32,34,36,40,44,46,48,56,60,66,68,78,80,88,98,100,

%T 102,104,108,116,118,120,128,136,148,152,164,170,174,176,182,188,190,

%U 192,196,200,204,212,220,226,232,234,238,246,250,252,258,260,262,266

%N Numbers k such that k^2 + 3 is a semiprime.

%C The semiprimes of this form are: 4, 39, 259, 327, 403, 579, 679, 1027, 1159, 1299, 1603, 1939, 2119, 2307, 3139, 3603, 4359, 4627, ...

%H Vincenzo Librandi, <a href="/A242331/b242331.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[300], PrimeOmega[#^2 + 3] == 2 &]

%o (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [0..300] | IsSemiprime(s) where s is n^2+3];

%Y Cf. A049422, A049423, A085722, A242330, A242332, A242333.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, May 14 2014