// 1. možnosť:

let foo n =
    [1 .. n]
    |> List.choose
        (fun x ->
            match x * 2 + 3 with i when i > 30 -> Some i | _ -> None)

// 2. možnosť:

let bar n =
    let rec my acc = function
    | 0 -> acc
    | i ->
        let x = i * 2 + 3
        my (if x > 30 then x :: acc else acc) <| i - 1
    my [] n

// 3. možnosť:

let baz n = seq { for i in 1 .. n do
                    let i = i * 2 + 3
                    if i > 30 then yield i }