Write a function to find the nth tetrahedral number.
def tetrahedral_number(n): 
	return (n * (n + 1) * (n + 2)) / 6
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find the nth tetrahedral number.
def tetrahedral_number(n): 
	return (n * (n + 1) * (n + 2)) / 6[/INST]assert tetrahedral_number(5) == 35.0
assert tetrahedral_number(6) == 56.0
assert tetrahedral_number(7) == 84.0</s>