这个用Python for循环怎么算，

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这个该怎么算呢，求各位解答问一下吧，真的不会算是，太摊了呢，教一教我把，亲们

1.计算数列的和

def calculate_sum(n):
    a1 = 1
    a2 = 1
    sum = a1 + a2
    for i in range(3, n+1):
        an = a1 + a2
        sum += an
        a1 = a2
        a2 = an
    return sum

2.计算调和级数的和

def calculate_harmonic_sum(n):
    sum = 0
    for i in range(1, n+1):
        sum += 1/i
    return sum

3.计算交替和


def calculate_alternate_sum(n):
    sum = 0
    sign = 1
    for i in range(1, n+1):
        sum += sign * 1/i
        sign *= -1
    return sum

4.寻找数列规律并计算其和


def calculate_sequence_sum(n):
    a1 = 3
    sum = a1
    for i in range(2, n+1):
        an = 2**(i-1) + 1
        sum += an
    return sum

帮你做第一题吧，别的你采纳了另外提问再说。

def feb(n):
    if n <= 2: 
        return 1
    return feb(n - 1) + feb(n - 2)
n = int(input("n:"))
sum = 0
for i in range(n):
    sum += feb(n + 1)
print(sum)