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%I #22 Sep 08 2022 08:45:39
%S 0,3,5,8,12,13,14,16,18,19,20,23,25,26,28,31,33,36,37,38,39,40,43,44,
%T 47,48,50,53,54,57,58,60,61,63,66,67,68,69,70,73,74,75,76,77,78,80,82,
%U 83,84,88,89,91,93,95,96,98
%N Numbers n such that 18*n+1 is not prime.
%H Vincenzo Librandi, <a href="/A153400/b153400.txt">Table of n, a(n) for n = 1..1000</a>
%e Distribution of the positive terms in the following triangular array:
%e *;
%e *,*;
%e *,*,*;
%e *,*,*,*;
%e *,3,*,*,*;
%e *,*,5,*,*,*;
%e *,*,*,*,*,*,*;
%e *,*,*,*,*,*,*,16;
%e *,*,*,*,*,*,*,*,20;
%e *,*,*,*,*,*,*,*,*,*;
%e *,*,*,*,14,*,*,*,*,*,*; etc.
%e where * marks the noninteger values of (2*h*k + k + h)/9 with h >= k >= 1. - _Vincenzo Librandi_, Jan 14 2013
%t Select[Range[0, 200], !PrimeQ[18 # + 1] &] (* _Vincenzo Librandi_, Jan 14 2013 *)
%o (Magma) [n: n in [0..150] | not IsPrime(18*n+1)]; // _Vincenzo Librandi_, Jan 14 2013
%Y Cf. A111094.
%K nonn,easy
%O 1,2
%A _Vincenzo Librandi_, Dec 25 2008
%E 0 added by _Arkadiusz Wesolowski_, Aug 03 2011