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 A300956 #10 Mar 20 2018 04:09:48
%S A300956 0,2,1,18,20,19,9,11,10,6,8,7,24,26,25,15,17,16,3,5,4,21,23,22,12,14,
%T A300956 13,774840978,774840980,774840979,774840996,774840998,774840997,
%U A300956 774840987,774840989,774840988,774840984,774840986,774840985,774841002,774841004
%N A300956 a(0) = 0, a(1) = 2, a(2) = 1, and for any n > 2 with ternary representation n = Sum_{i=0..k} t_i * 3^i, a(n) = Sum_{i=0..k} a(t_i) * 3^a(i).
%C A300956 This sequence is a self-inverse permutation of the natural numbers.
%C A300956 This sequence has connections with A300955.
%C A300956 This sequence has infinitely many fixed points (A300958); for any k >= 0, at least one of k or 3^k + 2 * 3^a(k) is a fixed point.
%H A300956 Rémy Sigrist, <a href="/A300956/b300956.txt">Table of n, a(n) for n = 0..10000</a>
%H A300956 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%F A300956 A160384(a(n)) = A160384(n).
%F A300956 a(a(n)) = n.
%o A300956 (PARI) a(n) = my (t=Vecrev(digits(n,3))); sum(i=0, #t-1, if (t[i+1]==1, 2, t[i+1]==2, 1, 0) * 3 ^ a(i))
%Y A300956 Cf. A160384, A300955, A300958 (fixed points).
%K A300956 nonn,base
%O A300956 0,2
%A A300956 _Rémy Sigrist_, Mar 17 2018