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A308714
Decimal expansion of 2*Pi*sech(sqrt(5/3)*Pi/2)/3.
2
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, 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, 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
OFFSET
0,1
FORMULA
Equals Product_{k>=2} (1 - 1/(3*k*(k - 1)/2 + 1)).
Equals Product_{k>=2} (1 - 1/A005448(k)).
EXAMPLE
0.5419123258325301299411023662126578003950258848928...
MATHEMATICA
RealDigits[2 Pi Sech[Sqrt[5/3] Pi/2]/3, 10, 120][[1]]
PROG
(PARI) 2*Pi*(1/cosh(sqrt(5/3)*Pi/2))/3 \\ Michel Marcus, Jun 20 2019
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Ilya Gutkovskiy, Jun 19 2019
STATUS
approved