Nth Tribonacci Number

Statement

Tribonacci numbers are a sequence of numbers where each number is the sum of the three preceding numbers. Your task is to find the $n^{th}$ Tribonacci number.

The Tribonacci sequence is defined as:

$T_0 = 0,\space T_1 = 1,\space T_2 = 1$, and $\space T_n = T_{n-1} + T_{n-2} + T_{n-3}, \space$

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