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 A338243 #9 Oct 18 2020 22:32:47
%S A338243 0,1,3,2,4,9,8,7,6,5,10,12,11,13,27,26,25,24,23,19,21,20,22,18,17,16,
%T A338243 15,14,28,30,29,31,36,35,34,33,32,37,39,38,40,81,80,79,78,77,73,75,74,
%U A338243 76,72,71,70,69,68,55,57,56,58,63,62,61,60,59,64,66,65,67
%N A338243 a(0) = 0, a(n) = A338241(2*n-1) for any n > 0.
%C A338243 This sequence is a self-inverse permutation of the nonnegative integers.
%H A338243 Rémy Sigrist, <a href="/A338243/b338243.txt">Table of n, a(n) for n = 0..6560</a>
%H A338243 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%e A338243 a(7) = A338241(13) = 7.
%o A338243 (PARI) b(n) = { if (n==0, return (0), my (d=n%3, m=n\3); if (d==0, 3*b(m), d==1, 1-3*b(m), 3*b(m)-1)) }
%o A338243 a(n) = if (n==0, 0, b(2*n-1))
%Y A338243 Cf. A338241, A338242.
%K A338243 nonn
%O A338243 0,3
%A A338243 _Rémy Sigrist_, Oct 18 2020