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 A153347 Numbers n>0 such that 7*n-4 is not prime. 1

%I

%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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Last modified May 10 14:32 EDT 2021. Contains 343771 sequences. (Running on oeis4.)