OFFSET
1,1
COMMENTS
Value very close to A193081.
FORMULA
EXAMPLE
4.87071896189479740325580288922801180768723798317416757630477557161789...
MAPLE
evalf(Sum(1-cos(Pi/n), n=1..infinity), 120);
MATHEMATICA
RealDigits[NSum[1 - Cos[Pi/n], {n, 1, Infinity}, WorkingPrecision -> 120, NSumTerms -> 10000, PrecisionGoal -> 120, Method -> {"NIntegrate", "MaxRecursion" -> 100}]][[1]] (* Be aware that NSum[1 - Cos[Pi/n], {n, 1, Infinity}, WorkingPrecision -> 120] or N[Sum[1 - Cos[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, 1-cos(Pi/n))
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Vaclav Kotesovec, Mar 01 2016
STATUS
approved