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 A259431 #14 Sep 04 2021 08:26:06
%S A259431 1,2,3,5,4,9,7,6,17,13,10,11,33,8,25,19,18,21,65,14,15,49,12,37,35,34,
%T A259431 41,129,26,27,29,20,97,23,22,73,69,66,67,81,16,257,51,50,53,57,38,39,
%U A259431 193,36,45,43,42,145,137,130,131,133,28,161,31,30,513,101,98
%N A259431 Inverse of permutation in A183209.
%H A259431 Alois P. Heinz, <a href="/A259431/b259431.txt">Table of n, a(n) for n = 1..10000</a>
%H A259431 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a>
%t A259431 b[n_] := b[n] = If[n==1, 1, If[EvenQ[n], 3b[n/2]-1, Floor[3b[(n+1)/2]/2]]];
%t A259431 a[n_] := Module[{k = 1}, While[n != b[k], k++]; k];
%t A259431 Array[a, 100] (* _Jean-François Alcover_, Sep 04 2021 *)
%o A259431 (Haskell)
%o A259431 import Data.List (elemIndex); import Data.Maybe (fromJust)
%o A259431 a259431 = (+ 1) . fromJust . (`elemIndex` a183209_list)
%o A259431 -- _Reinhard Zumkeller_, Jun 27 2015
%Y A259431 Cf. A183209.
%K A259431 nonn,look
%O A259431 1,2
%A A259431 _Alois P. Heinz_, Jun 26 2015