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 A338242 #10 Oct 18 2020 22:32:41
%S A338242 0,1,2,3,4,8,6,7,5,9,10,11,12,13,26,24,25,23,18,19,20,21,22,17,15,16,
%T A338242 14,27,28,29,30,31,35,33,34,32,36,37,38,39,40,80,78,79,77,72,73,74,75,
%U A338242 76,71,69,70,68,54,55,56,57,58,62,60,61,59,63,64,65,66,67
%N A338242 a(n) = -A338241(2*n) for any n >= 0.
%C A338242 This sequence is a self-inverse permutation of the nonnegative integers.
%H A338242 Rémy Sigrist, <a href="/A338242/b338242.txt">Table of n, a(n) for n = 0..6560</a>
%H A338242 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%e A338242 a(7) = -A338241(14) = 7.
%o A338242 (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 A338242 a(n) = -b(2*n)
%Y A338242 Cf. A338241, A338243.
%K A338242 nonn
%O A338242 0,3
%A A338242 _Rémy Sigrist_, Oct 18 2020