OFFSET
1,1
FORMULA
Equals Sum_{k>=2} (-1)^k * Pi^(2*k-1) * Zeta(2*k-1) / (2*k-1)!, where Zeta is the Riemann zeta function.
EXAMPLE
4.096434891501739832220234588626055495928144165119120475644486640639751...
MAPLE
evalf(Sum(Pi/n - sin(Pi/n), n=1..infinity), 120);
MATHEMATICA
RealDigits[NSum[Pi/n - Sin[Pi/n], {n, 1, Infinity}, WorkingPrecision->200, NSumTerms->10000, PrecisionGoal->120, Method->{"NIntegrate", "MaxRecursion"->100}]][[1]]
(* Be aware that N[Sum[Pi/n - Sin[Pi/n], {n, 1, Infinity}], 120] give an incorrect numerical result, only 25 decimal places are correct! *)
PROG
(PARI) default(realprecision, 120); sumpos(n=1, Pi/n - sin(Pi/n))
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Vaclav Kotesovec, Mar 04 2016
STATUS
approved