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