python例题及代码

1.题目;有一分数序列：2/1,3/2,5/3,8/5,13/8,21/13…求出这个数列的前20项之和。

a = 2
b = 1
s = 0
for i in range(1,21):
s += a/b
a = a + b
b = a - b
if i == 20:
print(s)

2题目：求1!+2!+3!+…+20!的和。

i = 1
s = 0
for o in range(1,21):
i = i * o
s = s + i
if o == 20:
print(s)

或者

s = 0
i = 1
o = 1
while o <= 20:
i *= o
o += 1
s += i
print(s)

3.题目：有1、2、3、4个数字，能组成多少个互不相同且无重复数字的三位数？都是多少？

t = 0
for i in range(1,5):
for o in range(1,5):
for a in range(1,5):
if i!=o and i!=a and o!=a:
s = 100*i + 10*o + a
print(s)
t = t + 1
print(t)