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 A133234 #8 Oct 30 2019 16:49:43
%S A133234 4,6,9,10,15,22,25,33,39,49,55,58,82,86,87,93,111,118,121,122,134,145,
%T A133234 185,194,201,202,206,215,237,247,274,287,298,299,303,305,314,334,335,
%U A133234 358,362,386,446,447,454,471,482,497,502,527,529,537,553,554,562,614
%N A133234 a(n) is least semiprime (not already in list) such that no 3-term subset forms an arithmetic progression.
%C A133234 This is to semiprimes A001358 as A131741 is to primes A000040.
%F A133234 a(1) = 4, a(2) = 6, a(n) = smallest semiprime such that there is no i < j < n with a(n) - a(j) = a(j) - a(i).
%t A133234 NextSemiprime[n_] := Block[{c = n + 1, f = 0}, While[Plus @@ Last /@ FactorInteger[c] != 2, c++ ]; c ]; f[l_List] := Block[{c, f = 0}, c = If[l == {}, 2, l[[ -1]]]; While[f == 0, c = NextSemiprime[c]; If[Intersection[l, l - (c - l)] == {}, f = 1]; ]; Append[l, c] ]; Nest[f, {}, 100] (* _Ray Chandler_, Nov 10 2007 *)
%Y A133234 Cf. A000040, A001358, A065825, A131741.
%K A133234 easy,nonn
%O A133234 1,1
%A A133234 _Jonathan Vos Post_, Oct 13 2007
%E A133234 More terms from _Ray Chandler_, Nov 10 2007