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  1. def reverse_factorial(num):
  2.     try:
  3.         float(num)
  4.     except:
  5. 	    return None
  6.     i = 2
  7.     if num == abs(num):
  8.         j = 1
  9.     else:
  10.         j = -1
  11.         num = abs(num)
  12.     while num > 1:
  13.         num /= i
  14.         i += 1
  15.     return j*i-1 if num == 1 else None
  16.  
  17. for num in [3628800,479001600,6,18,"a",1.2,-24]:
  18.     rev_fac = reverse_factorial(num)
  19.     print(num," NONE") if rev_fac is None else print(num," = ",rev_fac,"!",sep="")
Success #stdin #stdout 0.01s 9992KB
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3628800 = 10!
479001600 = 12!
6 = 3!
18  NONE
a  NONE
1.2  NONE
-24 = -6!
https://ideone.com/8wi01v
language:
Python 3 (python  3.9.5)
created:
7 years ago
visibility:
public

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