N-th Tribonacci Number
The Tribonacci sequence Tn is defined as follows:
T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.
Given n, return the value of Tn.
Example 1
Input
n = 4Output
4T_3 = 0 + 1 + 1 = 2, and T_4 = 1 + 1 + 2 = 4.
Example 2
Input
n = 25Output
1389537The 25th Tribonacci number is 1389537.
Constraints
- 0 <= n <= 37
- The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.