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 A353306 #4 Apr 13 2022 16:50:17
%S A353306 1,3,4,9,12,27,36,81,108,193,243,324,346,436,579,729,972,1038,1308,
%T A353306 1522,1737,1867,2187,2353,2539,2916,3114,3493,3924,4234,4566,5211,
%U A353306 5601,5824,6286,6561,7059,7617,8748,9342,9446,9709,10479,10886,11756,11772,12702,13698,13772,14792,14806,15633,15745,16184,16803,17003
%N A353306 Numbers k such that 1 is in the transitive closure of the map x -> A353313(x) when starting iterating from x=k.
%o A353306 (PARI)
%o A353306 A353313(n) = { my(r=(n%3)); if(!r,n/3,((5*((n-r)/3)) + r + 3)); };
%o A353306 A353305(n) = { my(visited = Map(), m=0); for(j=1, oo, n = A353313(n); if(!m, m=n, m=min(m,n)); if(mapisdefined(visited, n), return(m), mapput(visited, n, j))); };
%o A353306 isA353306(n) = (1==A353305(n));
%Y A353306 Positions of ones in A353305.
%Y A353306 Subsequences: A000244, A003946, A211221.
%K A353306 nonn
%O A353306 1,2
%A A353306 _Antti Karttunen_, Apr 13 2022