let problem2 = 
    let rec fib n =
     match n with
     | 0     -> 0
     | 1 | 2 -> 1
     | n     -> (fib (n - 1)) + (fib (n - 2))    
    
    {1..35} |> Seq.map (fun x -> fib x)
        |> Seq.filter ( fun z -> (z < 1000000 && z % 2 = 0)) 
          |> Seq.sumByInt(fun y -> y)