python斐波那契数列求和20相，每次递推一项

# 方法一：使用循环
a, b = 0, 1
sum = 0
for i in range(20):
a, b = b, a + b
sum += a
print(sum)

# 方法二：使用递归
def fib(n):
if n == 1 or n == 2:
return 1
else:
return fib(n-1) + fib(n-2)

sum = 0
for i in range(1, 21):
sum += fib(i)
print(sum)