Write a function to check whether the given number is undulating or not.
def is_undulating(n): 
	if (len(n) <= 2): 
		return False
	for i in range(2, len(n)): 
		if (n[i - 2] != n[i]): 
			return False
	return True
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to check whether the given number is undulating or not.
def is_undulating(n): 
	if (len(n) <= 2): 
		return False
	for i in range(2, len(n)): 
		if (n[i - 2] != n[i]): 
			return False
	return True[/INST]assert is_undulating("1212121") == True
assert is_undulating("1991") == False
assert is_undulating("121") == True</s>