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 A121542 #2 Mar 30 2012 17:26:21
%S A121542 5,6,7,8,9,10,12,14,16,18,20,22,23,24,26,27,28,30,31,32,34,35,36,38,
%T A121542 39,40,42,43,44,46,48,50,51,52,54,56,58,59,60,62,64,66,67,68,70,72,74,
%U A121542 75,76,78,80,82,83,84,86,88,90,91,92,94,95,96,98,99,100
%N A121542 Increasing sequence: "if n appears a*n+b does not", case a(1)=5, a=2, b=1.
%t A121542 s={5};With[{a=2,b=1},Do[If[FreeQ[s,(n-b)/a],AppendTo[s,n]],{n,6,100}]];s
%Y A121542 Cf. A121538, A121539, A121540, A121541.
%K A121542 nonn
%O A121542 1,1
%A A121542 _Zak Seidov_, Aug 08 2006