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 A072560 #18 Apr 04 2022 08:27:41
%S A072560 3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,1,1,3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,
%T A072560 1,1,3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,1,1,3,9,3,3,1,3,3,9,3,3,1,3,3,9,
%U A072560 3,1,1,1,3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,1,1,3,9,3,3,1,3,3,9,3,3,1,3,3,9,3
%N A072560 Denominators of w(n) where w(1)=w(2)=w(3)=1, w(n)=(w(n-1)*w(n-2)+(w(n-1)+w(n-2))/3) / w(n-3).
%C A072560 Sequence contains 1,3 or 9 only and is periodic with period (3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,1,1) of length 18.
%H A072560 <a href="/index/Rec#order_18">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1).
%e A072560 The sequence w() begins: 1, 1, 1, 5/3, 23/9, 17/3, 31/3, 25, 143/3, 353/3, 2039/9, 1685/3, 3251/3, 2689, 15571/3, ...
%t A072560 LinearRecurrence[{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},{3, 9, 3, 3, 1, 3, 3, 9, 3, 3, 1, 3, 3, 9, 3, 1, 1, 1},105] (* _Ray Chandler_, Aug 25 2015 *)
%t A072560 PadRight[{},120,{3,9,3,3,1,3,3,9,3,3,1,3,3,9,3,1,1,1}] (* _Harvey P. Dale_, Apr 04 2022 *)
%Y A072560 Cf. A072561, A072557.
%K A072560 nonn,frac
%O A072560 1,1
%A A072560 _Benoit Cloitre_, Aug 06 2002