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 A197809 #6 Feb 07 2025 16:44:04
%S A197809 1,3,4,0,5,2,5,3,0,8,1,9,7,3,9,8,4,4,7,8,6,7,6,0,6,2,8,4,9,9,6,0,6,6,
%T A197809 0,9,2,0,5,8,3,4,1,8,6,8,9,3,1,2,0,4,5,7,5,5,2,4,7,3,5,7,7,3,0,0,2,1,
%U A197809 3,0,7,8,1,3,0,4,2,1,6,6,7,3,0,3,4,7,6,9,9,7,5,6,5,9,9,9,0,8,2
%N A197809 Decimal expansion of x<0 having x^2+x=2*cos(x).
%C A197809 See A197737 for a guide to related sequences. The Mathematica program includes a graph.
%e A197809 negative: -1.3405253081973984478676062849960660920583...
%e A197809 positive: 0.7883968459929654290788209839820019122955...
%t A197809 a = 1; b = 1; c = 2;
%t A197809 f[x_] := a*x^2 + b*x; g[x_] := c*Cos[x]
%t A197809 Plot[{f[x], g[x]}, {x, -2, 1.5}]
%t A197809 r1 = x /. FindRoot[f[x] == g[x], {x, -1.5, -1.3}, WorkingPrecision -> 110]
%t A197809 RealDigits[r1] (* A197809 *)
%t A197809 r2 = x /. FindRoot[f[x] == g[x], {x, .78, .79}, WorkingPrecision -> 110]
%t A197809 RealDigits[r2] (* A197810 *)
%Y A197809 Cf. A197738.
%K A197809 nonn,cons
%O A197809 1,2
%A A197809 _Clark Kimberling_, Oct 20 2011