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

%I A153380 #20 Sep 08 2022 08:45:39
%S A153380 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 A153380 45,46,48,51,52,53,54,55,57,58,60,62,63,64,66,67,68,69,72,74,75,77,78,
%U A153380 79,81,84,86,87,88,89,90,93,94,95,96,97,98,99,102
%N A153380 Numbers n such that 10*n+9 is not prime.
%H A153380 Vincenzo Librandi, <a href="/A153380/b153380.txt">Table of n, a(n) for n = 1..1000</a>
%e A153380 Triangle begins:
%e A153380 0;
%e A153380 *,*;
%e A153380 *,*,4;
%e A153380 *,*,*,*;
%e A153380 *,*,*,*,*;
%e A153380 3,*,*,*,*,16;
%e A153380 *,*,*,*,*,*,*;
%e A153380 *,*,11,*,*,*,*,28;
%e A153380 *,*,*,*,20,*,*,*,*;
%e A153380 *,*,*,*,*,*,*,*,*,*;
%e A153380 6,*,*,*,*,29,*,*,*,*,52;
%e A153380 where * marks the non-integer values of (2*h*k + k + h - 4)/5 with h >= k >= 1. - _Vincenzo Librandi_, Jan 13 2013
%t A153380 Select[Range[0, 200], !PrimeQ[10 # + 9] &] (* _Vincenzo Librandi_, Jan 13 2013 *)
%o A153380 (Magma) [n: n in [0..150] | not IsPrime(10*n+9)]; // _Vincenzo Librandi_, Jan 13 2013
%Y A153380 Cf. A102700.
%K A153380 nonn,easy
%O A153380 1,2
%A A153380 _Vincenzo Librandi_, Dec 25 2008
%E A153380 0 added by _Arkadiusz Wesolowski_, Aug 03 2011