[0..9] |> List.map(fun i -> ((3-i%3)*3 +  (i/3 + 1)) % 10 )
    (*
        ((i+3)/3) + (3*i)

3 - i%3

        0 1 2 3 4 5 6 7 8 9 
        0 7 4 1 8 5 2 9 6 3 
     
        0 2 1 0 2 1 0 2 1 0 
        0 0 0 1 1 1 2 2 2 3
            1
i/3
 ((i+3)/3) + (3*i)


    *)
    