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 A197840 #6 Feb 07 2025 16:44:04
%S A197840 4,1,3,2,5,7,3,4,7,0,7,5,3,8,6,8,3,0,8,1,9,8,4,4,1,7,0,5,3,6,2,8,0,6,
%T A197840 1,2,1,0,5,5,1,8,5,3,1,5,3,8,1,1,1,8,0,1,1,7,2,6,0,4,0,6,9,4,2,3,3,7,
%U A197840 8,0,0,3,2,1,2,4,7,6,1,8,2,7,0,6,7,2,4,2,3,5,8,4,3,9,1,8,1,4,3
%N A197840 Decimal expansion of greatest x having x^2-4x=-cos(x).
%C A197840 See A197737 for a guide to related sequences. The Mathematica program includes a graph.
%e A197840 least x: 0.25839214437159967402757423807386027526101...
%e A197840 greatest x: 4.13257347075386830819844170536280612105...
%t A197840 a = 1; b = -4; c = -1;
%t A197840 f[x_] := a*x^2 + b*x; g[x_] := c*Cos[x]
%t A197840 Plot[{f[x], g[x]}, {x, -1, 5}]
%t A197840 r1 = x /. FindRoot[f[x] == g[x], {x, -4.2, -4.1}, WorkingPrecision -> 110]
%t A197840 RealDigits[r1] (* A197839 *)
%t A197840 r2 = x /. FindRoot[f[x] == g[x], {x, 4.1, 4.2}, WorkingPrecision -> 110]
%t A197840 RealDigits[r2] (* A197840 *)
%Y A197840 Cf. A197737.
%K A197840 nonn,cons
%O A197840 1,1
%A A197840 _Clark Kimberling_, Oct 20 2011