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 A352417 #12 Mar 31 2022 16:59:52
%S A352417 0,1,3,4,2,9,10,12,13,5,6,7,27,28,30,31,11,36,37,39,40,14,15,16,18,19,
%T A352417 21,22,8,81,82,84,85,29,90,91,93,94,32,33,34,108,109,111,112,38,117,
%U A352417 118,120,121,41,42,43,45,46,48,49,17,54,55,57,58,20,63,64,66
%N A352417 Inverse permutation to A352416.
%H A352417 Rémy Sigrist, <a href="/A352417/b352417.txt">Table of n, a(n) for n = 0..10000</a>
%H A352417 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%e A352417 A352416(7) = 11, so a(11) = 7.
%o A352417 (PARI) a(n) = { my (p=[1, 2]); for (k=2, oo, if (n<=p[k], my (v=0, d); while (n, v+=3^k*d=n\p[k]; if (d==2, v/=3); n-=d*p[k]; k--); return (v/3), p = concat(p, 2*p[k]+p[k-1]))) }
%Y A352417 Cf. A000129, A317204, A352416.
%K A352417 nonn,base
%O A352417 0,3
%A A352417 _Rémy Sigrist_, Mar 15 2022