let f i = 1.0 / (2.0 ** i)
let rec sum f n =
let x = f n
if x <= System.Double.Epsilon
then 0.0
else x + sum f (n + 1.0)
sum f 0.0 |> printfn "%A"
bGV0IGYgaSA9IDEuMCAvICgyLjAgKiogaSkKbGV0IHJlYyBzdW0gZiBuICA9IAogICAgbGV0IHggPSBmIG4KICAgIGlmIHggPD0gU3lzdGVtLkRvdWJsZS5FcHNpbG9uIAogICAgICAgICAgICB0aGVuIDAuMCAKICAgICAgICAgICAgZWxzZSB4ICsgc3VtIGYgKG4gKyAxLjApIApzdW0gZiAwLjAgfD4gcHJpbnRmbiAiJUEi