This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A153400 #22 Sep 08 2022 08:45:39 %S A153400 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 A153400 47,48,50,53,54,57,58,60,61,63,66,67,68,69,70,73,74,75,76,77,78,80,82, %U A153400 83,84,88,89,91,93,95,96,98 %N A153400 Numbers n such that 18*n+1 is not prime. %H A153400 Vincenzo Librandi, <a href="/A153400/b153400.txt">Table of n, a(n) for n = 1..1000</a> %e A153400 Distribution of the positive terms in the following triangular array: %e A153400 *; %e A153400 *,*; %e A153400 *,*,*; %e A153400 *,*,*,*; %e A153400 *,3,*,*,*; %e A153400 *,*,5,*,*,*; %e A153400 *,*,*,*,*,*,*; %e A153400 *,*,*,*,*,*,*,16; %e A153400 *,*,*,*,*,*,*,*,20; %e A153400 *,*,*,*,*,*,*,*,*,*; %e A153400 *,*,*,*,14,*,*,*,*,*,*; etc. %e A153400 where * marks the noninteger values of (2*h*k + k + h)/9 with h >= k >= 1. - _Vincenzo Librandi_, Jan 14 2013 %t A153400 Select[Range[0, 200], !PrimeQ[18 # + 1] &] (* _Vincenzo Librandi_, Jan 14 2013 *) %o A153400 (Magma) [n: n in [0..150] | not IsPrime(18*n+1)]; // _Vincenzo Librandi_, Jan 14 2013 %Y A153400 Cf. A111094. %K A153400 nonn,easy %O A153400 1,2 %A A153400 _Vincenzo Librandi_, Dec 25 2008 %E A153400 0 added by _Arkadiusz Wesolowski_, Aug 03 2011