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 A175904 #6 Mar 31 2012 10:22:16
%S A175904 2,3,6,8,9,10,12,14,15,16,18,20,21,22,24,27,28,30,32,33,36,38,39,40,
%T A175904 42,44,45,46,47,48,50,52,54,57,58,60,62,63,64,66,68,69,70,72,73,74,75,
%U A175904 77,78,80,82,84,85,86,87,88,90,93,94,95,96,98,99
%N A175904 Numbers m for which the set of prime divisors of m^2-1 is unique.
%C A175904 Complement of A175903. A proof for the presence of the first 63 terms (for which the largest prime divisor is < 100) follows along the lines of the comment in A175607.
%e A175904 The unique prime factor sets are {3} (m=2), {2} (m=3), {5,7} (m=6), {3,7} (m=8), {2,5} (m=9) etc.
%t A175904 aa = {}; bb = {}; cc = {}; ff = {}; Do[k = n^2 - 1; kk = FactorInteger[k]; b = {}; Do[AppendTo[b, kk[[m]][[1]]], {m, 1, Length[kk]}]; dd = Position[aa, b]; If[dd == {}, AppendTo[cc, n]; AppendTo[aa, b], AppendTo[ff, n]; AppendTo[bb, cc[[dd[[1]][[1]]]]]], {n, 2, 1000000}]; jj=Table[n,{2,99}]; ss=Union[bb,ff]; Take[Complement[jj,ss],63] (*Artur Jasinski*)
%Y A175904 Cf. A175607, A175901 - A175904, A181447 - A181471.
%K A175904 nonn
%O A175904 1,1
%A A175904 _Artur Jasinski_, Oct 12 2010, Oct 21 2010