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 A126881 #9 Oct 10 2019 13:40:07
%S A126881 1,2,2,3,5,7,8,9,17,25,26,32,69,137,214,215,433,553,554,654,1311,3967,
%T A126881 6565,6566,8979,21267,33151,53216,53217,106497,161963,242965,244832,
%U A126881 306046,714759,1579093,2396450,2420102,7278679,14557369,14778071
%N A126881 a(1)=1, a(2)=2. a(n) is the a(n-1)th integer from among those positive integers coprime to a(n-2).
%e A126881 a(4)=3, a(5)=5. So a(6) is the 5th positive integer which is coprime to 3. 3 is coprime to 1,2,4,5,7,8,10,11,... So a(6) is the 5th of these, which is 7.
%t A126881 f[m_, n_] := Block[{k = 0, c = n},While[c > 0,k++;While[GCD[k, m] > 1, k++ ];c--;];k];g[l_] := Append[l, f[l[[ -2]], l[[ -1]]]];Nest[g, {1, 2}, 40] (* _Ray Chandler_, Dec 31 2006 *)
%Y A126881 Cf. A126882.
%K A126881 nonn
%O A126881 1,2
%A A126881 _Leroy Quet_, Dec 29 2006
%E A126881 Extended by _Ray Chandler_, Dec 31 2006