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A242333 Numbers k such that k^2 + 5 is a semiprime. 5

%I #11 Sep 08 2022 08:46:08

%S 1,2,3,4,8,9,14,18,21,22,24,26,27,28,30,33,42,44,51,54,57,58,62,63,64,

%T 68,69,82,84,86,90,93,98,99,102,104,108,111,118,132,134,138,144,152,

%U 154,156,166,174,177,180,183,184,186,188,189,194,208,210,212,216

%N Numbers k such that k^2 + 5 is a semiprime.

%C The semiprimes of this form are: 6, 9, 14, 21, 69, 86, 201, 329, 446, 489, 581, 681, 734, 789, 905, 1094, 1769, 1941, 2606, 2921, 3254, ...

%H Vincenzo Librandi, <a href="/A242333/b242333.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[0, 300], PrimeOmega[#^2 + 5] == 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+5];

%Y Cf. A056905, A078402, A085722, A242330, A242331, A242332.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, May 14 2014

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)