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A308718
Decimal expansion of Pi*sech(Pi/2)/2.
3
6, 2, 6, 0, 2, 0, 1, 6, 5, 6, 2, 6, 0, 7, 3, 8, 1, 1, 5, 4, 4, 1, 7, 1, 4, 9, 8, 2, 1, 6, 3, 4, 4, 4, 3, 0, 7, 5, 8, 3, 5, 7, 7, 8, 5, 5, 9, 1, 7, 0, 3, 6, 5, 4, 5, 5, 3, 3, 5, 9, 8, 7, 9, 7, 1, 6, 9, 8, 0, 3, 7, 4, 5, 6, 6, 0, 8, 7, 3, 1, 7, 2, 1, 6, 2, 7, 0, 3, 6, 4, 5, 1, 4, 5, 1, 6, 2, 8, 1, 3, 2, 8, 3, 4, 9, 3, 4, 0, 2, 1, 2, 9, 2, 4, 8, 5, 5, 8, 1, 7
OFFSET
0,1
FORMULA
Equals Product_{k>=1} 1/(1 - (-1)^k/k^2).
Equals Product_{k>=1} (1 - 1/(2*k*(k + 1) + 1)).
Equals Product_{k>=1} (1 - 1/A001844(k)).
Equals Integral_{x=0..oo} cos(x)/cosh(x) dx. - Amiram Eldar, Aug 10 2020
EXAMPLE
0.6260201656260738115441714982163444307583577855917...
MATHEMATICA
RealDigits[Pi Sech[Pi/2]/2, 10, 120][[1]]
PROG
(PARI) Pi*(1/cosh(Pi/2))/2 \\ Michel Marcus, Jun 20 2019
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Ilya Gutkovskiy, Jun 19 2019
STATUS
approved