let rec divisible n =   
    let divbyall20 k = 
        let lista = Seq.map (fun x -> k % x ) {1..20}
        if (Seq.sumByInt (fun x -> x) lista) = 0 then true
        else false
    if divbyall20 n then n
    else divisible (n + 20)

printf "Problem 5: %d\n" (divisible 20)