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 A153380 Numbers n such that 10*n+9 is not prime. 1

%I

%S 0,3,4,6,9,11,12,15,16,18,20,21,24,25,27,28,29,30,31,32,33,36,39,42,

%T 45,46,48,51,52,53,54,55,57,58,60,62,63,64,66,67,68,69,72,74,75,77,78,

%U 79,81,84,86,87,88,89,90,93,94,95,96,97,98,99,102

%N Numbers n such that 10*n+9 is not prime.

%H Vincenzo Librandi, <a href="/A153380/b153380.txt">Table of n, a(n) for n = 1..1000</a>

%e Triangle begins:

%e 0;

%e *,*;

%e *,*,4;

%e *,*,*,*;

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

%e 3,*,*,*,*,16;

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

%e *,*,11,*,*,*,*,28;

%e *,*,*,*,20,*,*,*,*;

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

%e 6,*,*,*,*,29,*,*,*,*,52;

%e where * marks the non-integer values of (2*h*k + k + h - 4)/5 with h >= k >= 1. - _Vincenzo Librandi_, Jan 13 2013

%t Select[Range[0, 200], !PrimeQ[10 # + 9] &] (* _Vincenzo Librandi_, Jan 13 2013 *)

%o (MAGMA) [n: n in [0..150] | not IsPrime(10*n+9)]; // _Vincenzo Librandi_, Jan 13 2013

%Y Cf. A102700.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Dec 25 2008