Crivo de Eratostenes ainda lento...

gistfile1.fs

open System
open System.Collections.Generic

let sieve n = 
    seq {
        let hash = new HashSet<int64>()
        yield 2L
        for k in 3L..2L..System.Int64.MaxValue do
            if not (hash.Contains k) then
                yield k
            for j in k..k..n do 
                hash.Add(j) |> ignore
    }