Question: 
Write a function to calculate the nth pell number.


Model's Code:
def get_pell(n):
    if n == 0:
        return 0
    elif n == 1:
        return 1
    else:
        pell_numbers = [0, 1]
        for i in range(2, n + 1):
            next_pell = 2 * pell_numbers[i - 1] + pell_numbers[i - 2]
            pell_numbers.append(next_pell)
        return pell_numbers[n]



Sample Correct Code:
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 


Asserts:
assert get_pell(4) == 12
assert get_pell(7) == 169
assert get_pell(8) == 408


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

Test 169 of 974: 124/169 (73.37278106508876%): success