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 A268731 #11 Nov 19 2023 21:17:19
%S A268731 1,6,1,1,1,1,1,18,1,6,1,1,16,16,1,1,1,1,6,6,1,1,1,22,1,3,1,1,1,13,1,6,
%T A268731 6,6,6,6,6,16,1,108,1,28,1,1,1,6,2,1,1,1,2,2,6,6,18,1,18,1,18,18,53,
%U A268731 53,1,3,3,3,6,6,6,16,2,22,2,6,2,2,6,6,1,2,2,2
%N A268731 Period of the decimal expansion of 1/h(n) where h(n) is the length of the finite sequence {n, f(n), f(f(n)),...,1} in the Collatz (or 3n + 1) problem.
%C A268731 a(n) = A007732(A006577(n)).
%H A268731 Michel Lagneau, <a href="/A268731/b268731.txt">Table of n, a(n) for n = 2..9999</a>
%e A268731 a(3) = 6 because A007732(A006577(3)) = A007732(7) = 6.
%t A268731 f[n_]:=Module[{a=n,k=0},While[a!=1,k++;If[EvenQ[a],a=a/2,a=a*3+1]];k]; Table[r = f[n]/2^IntegerExponent[f[n], 2]/5^IntegerExponent[f[n], 5]; MultiplicativeOrder[10, r], {n, 2,100}]
%Y A268731 Cf. A006577, A007732.
%K A268731 nonn,base
%O A268731 2,2
%A A268731 _Michel Lagneau_, Feb 12 2016