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A181766 Numbers k such that 3*k + 7 is not prime.

%I A181766 #21 Sep 08 2022 08:45:54
%S A181766 1,3,5,6,7,9,11,13,14,15,16,17,19,21,23,25,26,27,28,29,31,33,35,36,37,
%T A181766 38,39,41,42,43,45,46,47,49,51,53,54,55,56,57,59,60,61,63,65,66,67,69,
%U A181766 70,71,73,75,76,77,79,80,81,82,83,84,85,86,87,89,91,93,94,95,96,97,98
%N A181766 Numbers k such that 3*k + 7 is not prime.
%C A181766 One less than the associated value in A153282, two less than A153309. - _R. J. Mathar_, Jan 05 2011
%H A181766 Vincenzo Librandi, <a href="/A181766/b181766.txt">Table of n, a(n) for n = 1..1000</a>
%e A181766 Distribution of the even terms in the following triangular array:
%e A181766 *;
%e A181766 *, 6;
%e A181766 *, *,14;
%e A181766 *, *,*,*;
%e A181766 *,16,*,*,38;
%e A181766 *,*,28,*,*,54;
%e A181766 *,*, *,*,*, *,*;
%e A181766 *,26,*,*,60,*,*,94;
%e A181766 *,*,42,*,*,80,*,*,118;
%e A181766 *,*,*, *,*,*, *,*, *, *;
%e A181766 *,36,*,*,82,*,*,128,*,*,174;
%e A181766 *,*,56,*,*,106,*,*,156,*,*,206; etc.
%e A181766 where * marks the non-integer values of (4*h*k + 2*k + 2*h - 6)/3 with h >= k >= 1. - _Vincenzo Librandi_, Jan 15 2013
%t A181766 Select[Range[0, 100], !PrimeQ[3 # + 7] &] (* _Vincenzo Librandi_, Oct 15 2012 *)
%o A181766 (Magma) [n: n in [0..100] | not IsPrime(3*n + 7)]; // _Vincenzo Librandi_, Oct 15 2012
%Y A181766 Cf. A089953 (3*n+7 is a prime).
%Y A181766 Cf. A153282, A153309.
%K A181766 nonn,easy
%O A181766 1,2
%A A181766 _Vincenzo Librandi_