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 A081428 #6 Mar 30 2012 17:30:54
%S A081428 34549,86371,103613,120919,138059,149519,172583,172741,224563,276293,
%T A081428 282059,282143,293659,299417,316691,352399,368513,379903,397303,
%U A081428 403061,414577,451499,483179,486527,489431,500947,506537,517747,518047,541799
%N A081428 Class 9- primes.
%D A081428 R. K. Guy, Unsolved Problems in Number Theory, A18.
%H A081428 R. J. Mathar, <a href="/A081428/b081428.txt">Table of n, a(n) for n = 1..6505</a>
%t A081428 PrimeFactors[n_Integer] := Flatten[Table[ #[[1]], {1}] & /@ FactorInteger[n]]; f[n_Integer] := Block[{m = n}, If[m == 0, m = 1, While[ IntegerQ[m/2], m /= 2]; While[ IntegerQ[m/3], m /= 3]]; Apply[Times, PrimeFactors[m] - 1]]; ClassMinusNbr[n_] := Length[NestWhileList[f, n, UnsameQ, All]] - 3; Prime[ Select[ Range[50000], ClassMinusNbr[ Prime[ # ]] == 9 &]]
%Y A081428 Cf. A005113, A056637, A005109, A005110, A005111, A005112, A081424, A081425, A081426, A081427, A081429, A081430.
%K A081428 nonn
%O A081428 1,1
%A A081428 _Robert G. Wilson v_, Mar 20 2003