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%I #7 Jun 20 2019 02:56:44
%S 5,4,1,9,1,2,3,2,5,8,3,2,5,3,0,1,2,9,9,4,1,1,0,2,3,6,6,2,1,2,6,5,7,8,
%T 0,0,3,9,5,0,2,5,8,8,4,8,9,2,8,1,6,2,0,9,1,4,9,6,0,6,3,3,6,0,8,1,4,6,
%U 9,5,3,7,9,4,5,6,2,1,1,4,3,7,7,6,3,5,7,5,7,5,1,9,4,8,6,8,2,8,0,7,3,7,3,2,7,8,6,7,5,1,2,3,2,8,6,3,8,4,2,2
%N Decimal expansion of 2*Pi*sech(sqrt(5/3)*Pi/2)/3.
%F Equals Product_{k>=2} (1 - 1/(3*k*(k - 1)/2 + 1)).
%F Equals Product_{k>=2} (1 - 1/A005448(k)).
%e 0.5419123258325301299411023662126578003950258848928...
%t RealDigits[2 Pi Sech[Sqrt[5/3] Pi/2]/3, 10, 120][[1]]
%o (PARI) 2*Pi*(1/cosh(sqrt(5/3)*Pi/2))/3 \\ _Michel Marcus_, Jun 20 2019
%Y Cf. A005448, A308642, A308713.
%K nonn,cons
%O 0,1
%A _Ilya Gutkovskiy_, Jun 19 2019
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