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%I #37 Dec 15 2024 09:32:00
%S 3,6,1,8,0,3,3,9,8,8,7,4,9,8,9,4,8,4,8,2,0,4,5,8,6,8,3,4,3,6,5,6,3,8,
%T 1,1,7,7,2,0,3,0,9,1,7,9,8,0,5,7,6,2,8,6,2,1,3,5,4,4,8,6,2,2,7,0,5,2,
%U 6,0,4,6,2,8,1,8,9
%N Decimal expansion of 2 + phi, with the golden section phi from A001622.
%C In a regular pentagon, inscribed in a unit circle this equals twice the largest distance between a vertex and a midpoint of a side.
%C This is an integer in the quadratic number field Q(sqrt(5)).
%C Only the first digit differs from A001622.
%D Steven R. Finch, Mathematical Constants, Encyclopedia of Mathematics and its Applications, vol. 94, Cambridge University Press, 2003, Section 5.25, p. 417.
%H Sumit Kumar Jha, <a href="https://arxiv.org/abs/2112.12081">Two complementary relations for the Rogers-Ramanujan continued fraction</a>, arXiv:2112.12081 [math.NT], 2021.
%F Equals 2 + A001622 = 1 + A104457 = 3 + A094214.
%F From _Christian Katzmann_, Mar 19 2018: (Start)
%F Equals Sum_{n>=0} (15*(2*n)!+40*n!^2)/(2*n!^2*3^(2*n+2)).
%F Equals 5/2 + Sum_{n>=0} 5*(2*n)!/(2*n!^2*3^(2*n+1)). (End)
%F Constant c = 2 + 2*cos(2*Pi/10). The linear fractional transformation z -> c - c/z has order 10, that is, z = c - c/(c - c/(c - c/(c - c/(c - c/(c - c/(c - c/(c - c/(c - c/(c - c/(z)))))))))). - _Peter Bala_, May 09 2024
%e 3.618033988749894848204586834365638117720309179805762862135448622705260462...
%t First@ RealDigits[2 + GoldenRatio, 10, 77] (* _Michael De Vlieger_, Jan 13 2018 *)
%o (PARI) (5 + sqrt(5))/2 \\ _Altug Alkan_, Mar 19 2018
%Y Cf. A001622, A094214, A104457, A176055, A020837.
%Y 2 + 2*cos(2*Pi/n): A104457 (n = 5), A116425 (n = 7), A332438 (n = 9), A019973 (n = 12).
%K nonn,cons,easy,changed
%O 1,1
%A _Wolfdieter Lang_, Jan 08 2018