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A178818 Decimal expansion of the diameter of the regular 7-gon (heptagon) of edge length 1.

%I A178818 #21 Aug 29 2025 13:33:05
%S A178818 2,0,7,6,5,2,1,3,9,6,5,7,2,3,3,6,5,6,7,1,6,3,5,3,8,8,6,1,4,8,5,8,4,0,
%T A178818 3,3,0,7,0,5,7,2,0,2,0,6,6,2,5,9,6,8,5,2,4,0,8,3,4,1,7,3,7,6,8,6,3,0,
%U A178818 2,8,4,8,7,0,6,4,5,9,7,7,1,7,4,6,4,4,1,7,5,5,1,5,9,7,6,0,6,2,2,5,3,5,4,8,8
%N A178818 Decimal expansion of the diameter of the regular 7-gon (heptagon) of edge length 1.
%H A178818 G. C. Greubel, <a href="/A178818/b178818.txt">Table of n, a(n) for n = 1..10000</a>
%H A178818 <a href="/index/Al#algebraic_06">Index entries for algebraic numbers, degree 6</a>.
%F A178818 Digits of cot(Pi/7).
%F A178818 Largest of the 6 real-valued roots of 7*x^6 -35*x^4 +21*x^2 -1=0. - _R. J. Mathar_, Aug 29 2025
%e A178818 2.07652139657233656716353886148584033070572020662596852408341737686302...
%p A178818 evalf[120](cot(Pi/7)); # _Muniru A Asiru_, Jan 22 2019
%t A178818 RealDigits[Cot[Pi/7],10, 100][[1]]
%o A178818 (PARI) default(realprecision, 100); cotan(Pi/7) \\ _G. C. Greubel_, Jan 22 2019
%o A178818 (Magma) SetDefaultRealField(RealField(100)); R:=RealField(); Cot(Pi(R)/7); // _G. C. Greubel_, Jan 22 2019
%o A178818 (Sage) numerical_approx(cot(pi/7), digits=100) # _G. C. Greubel_, Jan 22 2019
%Y A178818 Cf. A090488, A102771, A104956, A120011, A178809, A178816, A178817.
%K A178818 nonn,easy,cons,changed
%O A178818 1,1
%A A178818 _Vladimir Joseph Stephan Orlovsky_, Jun 16 2010