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%I #14 Sep 08 2022 08:46:08
%S 0,9,19,21,23,25,31,41,43,51,53,55,63,69,71,75,77,79,83,91,93,105,107,
%T 109,113,119,123,129,131,133,143,145,149,151,153,157,165,171,173,175,
%U 181,185,187,191,195,197,201,209,221,223,225,227,241,249,251,257,259
%N Numbers k such that k^2 + 4 is a semiprime.
%C The semiprimes of this form are: 4, 85, 365, 445, 533, 629, 965, 1685, 1853, 2605, 2813, 3029, 3973, 4765, 5045, 5629, 5933, 6245, ...
%H Vincenzo Librandi, <a href="/A242332/b242332.txt">Table of n, a(n) for n = 1..1000</a>
%t Select[Range[0, 300], PrimeOmega[#^2 + 4] == 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+4];
%Y Cf. A005473, A007591, A085722, A242330, A242331, A242333.
%K nonn
%O 1,2
%A _Vincenzo Librandi_, May 14 2014
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