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%I #14 Sep 08 2022 08:45:39
%S 2,4,6,7,8,10,12,13,14,16,17,18,19,20,21,22,24,25,26,27,28,30,31,32,
%T 34,36,37,38,40,42,43,44,46,47,48,49,50,52,54,55,56,57,58,60,61,62,63,
%U 64,65,66,67,68,70,71,72,73,74,76,77,78,79,80,82,84,85,86,87,88,90,91,92
%N Numbers n>0 such that 7*n-4 is not prime.
%H Vincenzo Librandi, <a href="/A153347/b153347.txt">Table of n, a(n) for n = 1..1000</a>
%e Distribution of the odd terms in the following triangular array:
%e *;
%e *,*;
%e *,*,*;
%e *,7,*,*;
%e *,*,*,*,*;
%e *,*,*,*,21,*;
%e 7,*,*,*,*,*,*;
%e *,*,*,*,*,*,37,*;
%e *,*,*,25,*,*,*,*,*;
%e *,*,*,*,*,*,*,*,*,*;
%e *,17,*,*,*,*,*,*,63,*,*;
%e *,*,*,*,*,47,*,*,*,*,*,*;
%e *,*,*,*,43,*,*,*,*,*,*,97,*;
%e 13,*,*,*,*,*,*,71,*,*,*,*,*,*; etc.
%e where * marks the non-integer values of (4*h*k + 2*k + 2*h + 5)/7 with h >= k >= 1. - _Vincenzo Librandi_, Jan 17 2013
%t Select[Range[1, 200], !PrimeQ[7 # - 4]&] (* _Vincenzo Librandi_, Jan 13 2013 *)
%o (Magma) [n: n in [1..150] | not IsPrime(7*n-4)]; // _Vincenzo Librandi_, Jan 13 2013
%Y Cf. A024903.
%K nonn,easy
%O 1,1
%A _Vincenzo Librandi_, Dec 24 2008
%E Erroneous comment deleted by _N. J. A. Sloane_, Jun 23 2010
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