%I #17 Oct 31 2023 08:24:04
%S 6,1,8,1,8,2,4,1,9,3,7,7,2,9,0,0,1,2,7,2,1,3,7,4,4,0,5,9,6,1,9,7,6,3,
%T 6,1,4,9,4,1,7,1,3,3,4,8,1,3,4,3,5,8,0,9,8,3,8,6,8,6,4,2,5,5,6,6,9,7,
%U 7,1,0,7,1,2,3,3,5,8,4,6,6,4,7,6,6,3,5,9,5,5,3,3,8,9,0,7,9,1,8,4,0,9,9,0,2
%N Decimal expansion of area of a regular 9-gon with unit edge length.
%H Stanislav Sykora, <a href="/A256853/b256853.txt">Table of n, a(n) for n = 1..2000</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Nonagon">Nonagon</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Regular_polygon">Regular polygon</a>
%H <a href="/index/Al#algebraic_06">Index entries for algebraic numbers, degree 6</a>
%F Equals (p/4)*cot(Pi/p), with p = 9.
%e 6.181824193772900127213744059619763614941713348134358098386864...
%t RealDigits[(9/4)*Cot[Pi/9], 10, 50][[1]] (* _G. C. Greubel_, Jul 03 2017 *)
%o (PARI) p=9; a=(p/4)*cotan(Pi/p) \\ Use realprecision in excess
%Y Cf. A000796, A019968, A120011 (p=3), A102771 (p=5), A104956 (p=6), A178817 (p=7), A090488 (p=8), A178816 (p=10), A256854 (p=11), A178809 (p=12).
%K nonn,cons
%O 1,1
%A _Stanislav Sykora_, Apr 12 2015
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