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 A255899 #22 Feb 19 2022 03:41:47
%S A255899 5,2,9,8,6,4,1,6,9,2,0,5,5,5,3,7,2,4,8,6,8,2,3,2,9,8,9,5,2,5,1,4,2,1,
%T A255899 3,7,3,0,0,3,8,0,1,3,2,0,8,2,7,2,8,9,0,5,7,5,7,4,8,9,7,8,6,5,8,4,1,8,
%U A255899 0,5,0,1,7,4,1,3,7,7,2,7,7,9,4,5,4,6,9,9,7,0,4,6,7,4,9,2,3,6,8,8,8,2,1,1,8
%N A255899 Decimal expansion of Mrs. Miniver's constant.
%C A255899 This constant is the solution to an elementary problem involving two overlapping circles, known as "Mrs. Miniver's problem" (cf. S. R. Finch, p. 487), the value of the solution being the distance between the centers of the two circles (see the picture by L. A. Graham in A192408).
%D A255899 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, p. 487.
%H A255899 Steven R. Finch, <a href="http://arxiv.org/abs/2001.00578">Errata and Addenda to Mathematical Constants</a>, arXiv:2001.00578 [math.HO], 2020-2021, p. 62.
%F A255899 The unique root of the equation 2*arccos(x/2) - (1/2)*x*sqrt(4 - x^2) = 2*Pi/3 in the interval [0,2].
%F A255899 Equals 2*cos(A336082 /2). - _Robert FERREOL_, Feb 18 2022
%e A255899 0.5298641692055537248682329895251421373003801320827289...
%t A255899 d = x /. FindRoot[2*ArcCos[x/2] - (1/2)*x*Sqrt[4 - x^2] == 2*Pi/3, {x, 1/2}, WorkingPrecision -> 105]; RealDigits[d] // First
%o A255899 (PARI) solve (x=0, 2, 2*acos(x/2) - (1/2)*x*sqrt(4 - x^2) - 2*Pi/3) \\ _Michel Marcus_, Mar 10 2015
%Y A255899 Cf. A192408.
%K A255899 nonn,cons,easy
%O A255899 0,1
%A A255899 _Jean-François Alcover_, Mar 10 2015