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%I #17 Jun 24 2021 13:44:40
%S 8,7,2,2,8,4,0,4,1,0,6,5,6,2,7,9,7,6,1,7,5,1,9,7,5,3,2,1,7,1,2,2,5,8,
%T 7,0,6,4,0,2,7,7,7,8,0,8,8,9,9,3,3,0,3,2,5,2,0,3,5,2,1,4,7,7,8,4,9,8,
%U 5,5,8,2,7,7,6,4,5,4,2,4,3,6,1,6,6,5,4,2,2,2,8,6,2,8,9,7,9,8,5,5,9,5,9,8,8,7,8
%N Decimal expansion of the total area of Ford circles.
%C Named after the American mathematician Lester Randolph Ford, Sr. (1886-1967). - _Amiram Eldar_, Jun 24 2021
%H L. R. Ford, <a href="https://www.jstor.org/stable/2302799">Fractions</a>, The American Mathematical Monthly, Vol. 45, No. 9 (1938), pp. 586-601.
%H Wieslaw Marszalek, <a href="https://doi.org/10.1007%2Fs00034-012-9392-3">Circuits with Oscillatory Hierarchical Farey Sequences and Fractal Properties</a>, Circuits Syst Signal Process, Vol. 31 (2012), pp. 1279-1296.
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/FordCircle.html">Ford Circle</a>.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Ford_circle">Ford circle</a>.
%F Equals (Pi/4) * Sum_{n >= 1} EulerPhi(n)/n^4.
%F Equals (Pi/4) * zeta(3)/zeta(4).
%F Equals 45*zeta(3) / (2*Pi^3).
%e 0.8722840410656279761751975321712258706402777808899330325203521...
%t RealDigits[Pi/4 * Zeta[3]/Zeta[4], 10, 107][[1]]
%o (PARI) Pi/4 * zeta(3)/zeta(4) \\ _Michel Marcus_, Dec 04 2016
%Y Cf. A000010, A002117, A013662.
%K nonn,cons
%O 0,1
%A _Jean-François Alcover_, Dec 04 2016
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