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 A195559 #8 Mar 09 2014 13:40:27
%S A195559 1,4,91,240,840,989,5396,117719,312120,1089720,1284121,7003804,
%T A195559 152799571,405130920,1414456320,1666787669,9090932396,198333725039,
%U A195559 525859622640,1835963213040,2163489110641,11800023246004,257437022301451
%N A195559 Denominators a(n) of Pythagorean approximations b(n)/a(n) to 2/3.
%C A195559 See A195500 for a discussion and references.
%t A195559 r = 2/3; z = 25;
%t A195559 p[{f_, n_}] := (#1[[2]]/#1[[
%t A195559 1]] &)[({2 #1[[1]] #1[[2]], #1[[1]]^2 - #1[[
%t A195559 2]]^2} &)[({Numerator[#1], Denominator[#1]} &)[
%t A195559 Array[FromContinuedFraction[
%t A195559 ContinuedFraction[(#1 + Sqrt[1 + #1^2] &)[f], #1]] &, {n}]]]];
%t A195559 {a, b} = ({Denominator[#1], Numerator[#1]} &)[
%t A195559 p[{r, z}]] (* A195559, A195560 *)
%t A195559 Sqrt[a^2 + b^2] (* A195561 *)
%t A195559 (* _Peter J. C. Moses_, Sep 02 2011 *)
%Y A195559 Cf. A195500, A195560, A195561.
%K A195559 nonn
%O A195559 1,2
%A A195559 _Clark Kimberling_, Sep 21 2011