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 A102570 #14 May 03 2023 09:54:43
%S A102570 1,2,3,4,5,6,10,12,7,14,8,16,18,9,20,11,48,13,28,15,31,17,36,19,38,21,
%T A102570 22,80,44,23,43,24,25,26,51,52,27,55,29,30,58,60,32,64,66,33,34,70,68,
%U A102570 35,144,37,76,39,79,40,41,42,87,84,45,46,94,92,47,192,49,50,99,100,53
%N A102570 a(n) = A102568(A102568(n)).
%C A102570 Inverse permutation to A102571.
%H A102570 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%t A102570 nmax = 100;
%t A102570 A102568 = Nest[Append[#, If[#[[-1]] == #[[-2]]+1, 2 #[[-1]], Min[Complement[Range[Max[#]+1], #]]]]&, {1, 2}, 2 nmax];
%t A102570 a[n_ /; n <= Length[A102568]] := A102568[[A102568[[n]]]];
%t A102570 Table[a[n], {n, 1, nmax}] (* _Jean-François Alcover_, May 03 2023, after _Ivan Neretin_ in A102568 *)
%Y A102570 Cf. A102568, A102571.
%K A102570 nonn
%O A102570 1,2
%A A102570 _Reinhard Zumkeller_, Jan 15 2005