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 A021670 #17 Jul 08 2025 08:46:11
%S A021670 0,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,
%T A021670 0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,
%U A021670 1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1,5,0,1
%N A021670 Decimal expansion of 1/666.
%H A021670 Burkard Polster, <a href="http://plus.maths.org/issue52/features/polster/index.html">Juggling, maths and a beautiful mind</a>
%H A021670 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,1).
%t A021670 Join[{0,0},RealDigits[1/666,10,120][[1]]] (* or *) PadRight[{0,0,1},111,{5,0,1}] (* _Harvey P. Dale_, Oct 17 2011 *)
%o A021670 (PARI) a(n)=if(n,[5,0,1][n%3+1],0) \\ _Charles R Greathouse IV_, Jan 20 2012
%K A021670 nonn,cons,easy
%O A021670 0,4
%A A021670 _N. J. A. Sloane_