F# Finding Prime Number

let IsNotMultipleOf n x =
    x=n || x%n<>0

let rec RemoveAllMultiples listn listx =
    match listn with
    | head::tail -> RemoveAllMultiples tail (List.filter (IsNotMultipleOf head) listx)
    | [] -> listx

let GetPrimeTo n =
    let r= (int) ( sqrt(float n))
    RemoveAllMultiples  [2..r] [1..100]

printfn "%A" (GetPrimeTo 100)