Write a function to find the nth hexagonal number.
def hexagonal_num(n): 
	return n*(2*n - 1) 
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to find the nth hexagonal number.
def hexagonal_num(n): 
	return n*(2*n - 1) [/INST]assert hexagonal_num(10) == 190
assert hexagonal_num(5) == 45
assert hexagonal_num(7) == 91</s>