Algorithm for Magical sequence

The Magical Sequence

A Magical Sequence is defined as shown.

Magical[1] = 0
Magical[2] = 1
Magical[n] = 1*Magical[n-1] + 2*Magical[n-2] + 3*1, for n > 2

Given n (1 <= n <= 10 ), find Magical[n].

Example 1: input1: 3 Output: 4 Explanation:

Magical[n] = 1*Magical[n-1] + 2*Magical[n-2] + 3*1
    Magical[3] = 1*Magical[2] + 2*Magical[1] + 3*1
    Magical[3] = 1*1 + 2*0 + 3*1
    Magical[3] = 4