Write a function to calculate the nth pell number.
def get_pell(n): 
	if (n <= 2): 
		return n 
	a = 1
	b = 2
	for i in range(3, n+1): 
		c = 2 * b + a 
		a = b 
		b = c 
	return b 
<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to calculate the nth pell number.
def get_pell(n): 
	if (n <= 2): 
		return n 
	a = 1
	b = 2
	for i in range(3, n+1): 
		c = 2 * b + a 
		a = b 
		b = c 
	return b [/INST]assert get_pell(4) == 12
assert get_pell(7) == 169
assert get_pell(8) == 408</s>