Barebone F# Parallel programming

open System
let prog(i)=
    async {
    printfn "starting..%d" i
    do! Async.Sleep(i%5*1000)
    printfn "finished..%d" i
    }

let ret=
    [1..1000]
    |> Seq.map ( fun n->prog(n))
    |> Async.Parallel 
    |> Async.StartAsTask

Console.ReadLine() |> ignore