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Numbers n such that 7*n+3 is not prime.
1

%I #22 Sep 08 2022 08:45:40

%S 1,3,5,6,7,9,11,12,13,15,16,17,18,19,20,21,23,24,25,26,27,29,30,31,33,

%T 35,36,37,39,41,42,43,45,46,47,48,49,51,53,54,55,56,57,59,60,61,62,63,

%U 64,65,66,67,69,70,71,72,73,75,76,77,78,79

%N Numbers n such that 7*n+3 is not prime.

%C The even terms are the integer values of (4*h*k + 2*k + 2*h - 2)/7, where h and k are positive integers. - _Vincenzo Librandi_, Jan 17 2013

%C The corresponding composite numbers are 10, 24, 38, 45, 52, 66, 80, 87, 94, 108, 115, 122, 129, ... - _Michael B. Porter_, Jan 17 2013

%H Vincenzo Librandi, <a href="/A154611/b154611.txt">Table of n, a(n) for n = 1..1000</a>

%t With[{nn=100},Sort[Join[Range[1,nn-1,2],Select[Range[0,nn,2], !PrimeQ[ 7#+3]&]]]] (* _Harvey P. Dale_, Aug 22 2012 *)

%t Select[Range[0, 100], !PrimeQ[7 # + 3]&] (* _Vincenzo Librandi_, Apr 05 2013 *)

%o (Magma) [n: n in [0..80] | not IsPrime(7*n+3)]; // _Vincenzo Librandi_, Apr 05 2013

%Y Cf. A089033, A045437, A017017.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Jan 15 2009

%E Erroneous comments deleted by _N. J. A. Sloane_, Jun 23 2010