# Fibonacci

The sequence below is Fibonacci sequence:

1, 1, 2, 5, 8, 13, 21, 35, ...

Fibonacci sequence has some characteristic that should be known. Let's say the th item of the sequence is , then:

We usually have or .

A convenient calculation of depends on following expressions:

This form represents items of Fibonacci sequence as the power of a matrix, so we can use Divide and Conquer to calculate in . Sepecifically, let's say we use to represent the matrix, if is even, can be gotten by:

Conversely, if is odd, we use .