階乗計算機

import math

# Built-in factorial
print(math.factorial(10))   # 3628800
print(math.factorial(50))   # exact large integer
print(math.factorial(100))  # 158-digit number

# Manual implementation
def factorial(n):
    if n == 0: return 1
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result

# Step-by-step display
n = 5
steps = " × ".join(str(i) for i in range(n, 0, -1))
print(f"{n}! = {steps} = {factorial(n)}")