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Numbers n such that 8n-9 is not prime.
1

%I #12 Sep 08 2022 08:45:40

%S 0,1,3,6,8,9,12,13,15,16,18,19,21,23,24,27,28,30,32,33,36,37,38,39,41,

%T 42,43,44,45,48,50,51,52,53,54,57,58,60,63,65,66,67,68,69,70,71,72,73,

%U 74,75,78,79,81,83,84,85,86,87,88,89,90

%N Numbers n such that 8n-9 is not prime.

%H Vincenzo Librandi, <a href="/A153769/b153769.txt">Table of n, a(n) for n = 1..1000</a>

%e Distribution of the terms > a(2) in the following triangular array:

%e *;

%e 3,*;

%e *,*,*;

%e *,*,9,*;

%e *,8,*,*,*;

%e 6,*,*,*,19,*;

%e *,*,*,18,*,*,*;

%e *,*,16,*,*,*,33,*;

%e *,13,*,*,*,32,*,*,*;

%e 9,*,*,*,30,*,*,*,51,*;

%e *,*,*,27,*,*,*,50,*,*,*;

%e *,*,23,*,*,*,48,*,*,*,73,*;

%e *,18,*,*,*,45,*,*,*,72,*,*,*;

%e 12,*,*,*,41,*,*,*,70,*,*,*,99,*; etc.

%e where * marks the non-integer values of (2*h*k + k + h + 5)/4 with h >= k >= 1. - _Vincenzo Librandi_, Jan 19 2013

%t lst={};Do[If[!PrimeQ[8*n-9],AppendTo[lst,n]],{n,0, 500}];lst (* _Vincenzo Librandi_, Jul 31 2012 *)

%t Select[Range[0,100],!PrimeQ[8#-9]&] (* _Harvey P. Dale_, Jun 08 2015 *)

%o (Magma) [n: n in [0..100]| not IsPrime(8*n-9)]; // _Vincenzo Librandi_, Jul 31 2012

%Y Cf. A153766.

%K nonn,easy

%O 1,3

%A _Vincenzo Librandi_, Jan 01 2009