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 A010477 #26 Nov 21 2023 05:52:46
%S A010477 4,5,8,2,5,7,5,6,9,4,9,5,5,8,4,0,0,0,6,5,8,8,0,4,7,1,9,3,7,2,8,0,0,8,
%T A010477 4,8,8,9,8,4,4,5,6,5,7,6,7,6,7,9,7,1,9,0,2,6,0,7,2,4,2,1,2,3,9,0,6,8,
%U A010477 6,8,4,2,5,5,4,7,7,7,0,8,8,6,6,0,4,3,6,1,5,5,9,4,9,3,4,4,5,0,3
%N A010477 Decimal expansion of square root of 21.
%C A010477 Continued fraction expansion is 4 followed by {1, 1, 2, 1, 1, 8} repeated. - _Harry J. Smith_, Jun 03 2009
%C A010477 The fundamntal algebraic (integer) number in the field Q(sqrt(21)) is (1 + sqrt(21))/2 = A222134. - _Wolfdieter Lang_, Nov 21 2023
%H A010477 Harry J. Smith, <a href="/A010477/b010477.txt">Table of n, a(n) for n = 1..20000</a>
%H A010477 <a href="http://gilkalai.files.wordpress.com/2011/02/root.png">Frankfurter Allgemeine Zeitung, Feb 09 2011</a> (in German)
%H A010477 <a href="/index/Al#algebraic_02">Index entries for algebraic numbers, degree 2</a>
%e A010477 4.582575694955840006588047193728008488984456576767971902607242123906868...
%t A010477 RealDigits[N[Sqrt[21],200]][[1]] (* _Vladimir Joseph Stephan Orlovsky_, Feb 22 2011 *)
%o A010477 (PARI) default(realprecision, 20080); x=sqrt(21); for (n=1, 20000, d=floor(x); x=(x-d)*10; write("b010477.txt", n, " ", d)); \\ _Harry J. Smith_, Jun 03 2009
%Y A010477 Cf. A010125 (continued fraction), A248249 (Egyptian fraction).
%Y A010477 Cf. A020778 (reciprocal), A222134.
%K A010477 nonn,easy,cons
%O A010477 1,1
%A A010477 _N. J. A. Sloane_