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tribonacci

Write a function tribonacci that takes in a number argument, n, and returns the n-th number of the Tribonacci sequence.

The 0-th and 1-st numbers of the sequence are both 0.

The 2-nd number of the sequence is 1.

To generate further numbers of the sequence, calculate the sum of previous three numbers.

Solve this recursively.

tribonacci(0) # -> 0

tribonacci(1) # -> 0

tribonacci(2) # -> 1

tribonacci(5) # -> 4

tribonacci(7) # -> 13

tribonacci(14) # -> 927

tribonacci(20) # -> 35890

tribonacci(37) # -> 1132436852

editor — tribonacci.py

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