Pythonで因数分解

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