条件：
①递归有最小值或有确定值
②fun(x) = ax * bfun(x-1) 类似规则
eg. n! :
①1! = 1
②n! = n* (n-1)!
def factorial (n):
if n==1: return 1
else:return n*factorial(n-1)
eg. x^n :
① n = 0 x^n = 1
②x^n = x*x^(n-1)
def power(x,n):
if n == 0: return 1
else: return x*power(x,n-1)
funcation eg. Armstrong Number: len(str(number)) = n str(number)[0]^n+str(number)[1]^n+str(number)[2]^n........ = number eg. 153 = 1^3+5^3+3^3
number = input('Enter your tested number: ')
temp = 0
digit=len(str(number))
power=digit
while digit>0:
temp += (int(str(number)[digit-1]))**power
print (temp)
digit -= 1
if temp == number: print ('yes',number,'is an Armstrong Number')
if temp != number: print ('no',number,'is not an Armstrong Number')