Question: 
Write a function to find the nth tetrahedral number.


Model's Code:
def tetrahedral_number(n):
    return n * (n + 1) * (n + 2) / 6



Sample Correct Code:
def tetrahedral_number(n): 
	return (n * (n + 1) * (n + 2)) / 6


Asserts:
assert tetrahedral_number(5) == 35.0
assert tetrahedral_number(6) == 56.0
assert tetrahedral_number(7) == 84.0


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 80 of 974: 61/80 (76.25%): success