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 A251545 #20 Sep 05 2018 14:45:35
%S A251545 4,9,21,25,26,33,58,82,85,93,95,111,115,129,177,213,237,265,267,309,
%T A251545 321,329,335,365,381,411,427,505,519,545,565,579,581,597,633,655,679,
%U A251545 687,699,723,753,755,785,789,831,835,879,895,921,951,973,985,1043,1047,1115,1135
%N A251545 A251544, sorted.
%C A251545 4, 9, and 25 are squares. It appears that all the remaining terms are the products of two distinct primes, usually both odd. (But not all such numbers occur, of course.)
%C A251545 It would be nice to have a characterization of these numbers that is independent of A098550.
%H A251545 David L. Applegate, Hans Havermann, Bob Selcoe, Vladimir Shevelev, N. J. A. Sloane, and Reinhard Zumkeller, <a href="http://arxiv.org/abs/1501.01669">The Yellowstone Permutation</a>, arXiv preprint arXiv:1501.01669, 2015 and <a href="https://cs.uwaterloo.ca/journals/JIS/VOL18/Sloane/sloane9.html">J. Int. Seq. 18 (2015) 15.6.7</a>.
%t A251545 terms = 56;
%t A251545 max = 15 terms;
%t A251545 f[lst_] := Block[{k = 4}, While[GCD[lst[[-2]], k] == 1 || GCD[lst[[-1]], k] > 1 || MemberQ[lst, k], k++]; Append[lst, k]];
%t A251545 A098550 = Nest[f, {1, 2, 3}, max - 3];
%t A251545 sel = Select[Transpose[{Range[max], A098550}], PrimeQ[#[[2]]]&][[All,1]]+2;
%t A251545 Sort[A098550[[sel]]][[1 ;; terms]] (* _Jean-François Alcover_, Sep 05 2018, after _Robert G. Wilson v_ in A098550 *)
%Y A251545 Cf. A098550, A251542-A251544, A253056.
%K A251545 nonn
%O A251545 1,1
%A A251545 _David Applegate_ and _N. J. A. Sloane_, Dec 16 2014