自然数 $n$ $(n\geq2)$ をPythonで因数分解します。

## 関数 factorization()

factorization.py

```
def factorization(n):
if n > 1 and n % 1 == 0:
for i in range(2, int(n**0.5)+1):
if n % i == 0:
print("%d = %i"%(n,i),end="")
m = n // i
j = 2
while j <= m:
if m % j == 0:
print("*%d"%j,end="")
m = m // j
j = 2
else:
j += 1
break
else:
print("%d is a prime number"%n,end="")
else:
print("error",end="")
print()
```

## 実行

合成数

```
>>> factorization(18)
18 = 2*3*3
```

素数

```
>>> factorization(97)
97 is a prime number
```

自然数でない場合、「error」が返されます。

```
>>> factorization(-3)
error
```

```
>>> factorization(2.1)
error
```

最後に

```
>>> for x in range(2,21):
... factorization(x)
...
2 is a prime number
3 is a prime number
4 = 2*2
5 is a prime number
6 = 2*3
7 is a prime number
8 = 2*2*2
9 = 3*3
10 = 2*5
11 is a prime number
12 = 2*2*3
13 is a prime number
14 = 2*7
15 = 3*5
16 = 2*2*2*2
17 is a prime number
18 = 2*3*3
19 is a prime number
20 = 2*2*5
```