type BiNodo = (Int,[(Integer,(Int,Integer))])

nivelArbolBiLista :: BiNodo -> BiNodo
nivelArbolBiLista (k,xs) = (k+1,concatMap g xs) where
    d = 2^k
    g (x,(n,y)) = [izq,der] where
        izq = (ii,(n,di))
        der = (id,(n+1,dd))
        (ii,id) = if even y then (x,x+d) else (x+d,x)
        di = if even y
            then quot y 2
            else quot (y + 3^n) 2
        dd = if odd y
            then quot (3*y + 1) 2
            else quot (3*y + 3^(n+1) + 1) 2

nivel n = secuencia !! n where
    secuencia = map (\ (_,xs) -> map (\ (a,(b,c)) -> (a,c)) xs) sec
    sec = iterate nivelArbolBiLista (2,[(3,(2,8))])