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%I A350885 #20 Jan 21 2022 10:25:25
%S A350885 1,9,1,5,3,1,5,1,0,8,7,2,0,5,7,1,5,2,7,5,0,0,5,5,4,8,2,0,8,6,4,0,9,4,
%T A350885 5,5,2,8,5,6,9,7,2,6,5,8,4,6,3,3,4,8,6,5,9,2,8,2,7,8,4,3,2,5,2,7,2,5,
%U A350885 8,4,5,4,0,3,1,2,5,6,2,6,1,7,3,5,6,6,1,7,0,4,5,4,4,2,0,4,6
%N A350885 Decimal expansion of 1 - 2*cotan(2).
%C A350885 The constant given in the name is computed using a telescopic sum coming from cotan(x) - 2*cotan(2*x) = tan(x).
%D A350885 J. Quinet, Cours élémentaire de Mathématiques Supérieures, Tome 3, Calcul intégral et Séries, Bordas, 1973, Exercice 7.36, pp 111 and 231.
%F A350885 Equals Sum_{m>=0} (1/2^m) * (tan(1/2^m)).
%F A350885 Equals (t^2+t-1)/t with t=A049471. - _Michel Marcus_, Jan 21 2022
%e A350885 1.915315108720571527500554820864094552856972658463348659...
%p A350885 evalf(1-2/tan(2),120);
%t A350885 RealDigits[1 - 2*Cot[2], 10, 100][[1]] (* _Amiram Eldar_, Jan 21 2022 *)
%o A350885 (PARI) 1-2*cotan(2) \\ _Michel Marcus_, Jan 21 2022
%Y A350885 Cf. A049471, A073449.
%K A350885 nonn,cons
%O A350885 1,2
%A A350885 _Bernard Schott_, Jan 21 2022

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