Auxiliary functions

primes2.fs

let filterRange predicate (i, j) =
    let results = ResizeArray(j-i+1) // reserve quite a lot of space.
    for k = i to j do
        if predicate k then results.Add(k)
    results.ToArray()

let indivisible divisors b =
    Array.forall (fun a -> b%a<>0) divisors