The above method actually takes formula_65 time for large n because addition of two integers with formula_66 bits each takes formula_66 time. (The "n"th fibonacci number has formula_66 bits.) Also, there is a closed form for the Fibonacci sequence, known as Binet's formula, from which the formula_19-th term can be computed in approximately formula_70 time, which is more efficient than the above dynamic programming technique. However, the simple recurrence directly gives the matrix form that leads to an approximately formula_71 algorithm by fast matrix exponentiation.