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Remainder (Posted on 2003-10-16) Difficulty: 3 of 5
If 'p' be a prime, then what is the remainder when (p - 1)! is divided by p?

See The Solution Submitted by Ravi Raja    
Rating: 3.8889 (9 votes)

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Solution full solution | Comment 4 of 10 |
Another restatement of the problem is:
Given:
(p-1)! ≡ m (mod p)

where:
  • p is a prime number,
  • ≡ means congruent (in modular arithmetic, having the same remainder when divided by some number), and
  • m is some integer between 0 and p-1 (the remainder)

What is m?
______________

This is a restatement of Wilson's theorem. The answer (as stated three times before) is p-1, which of course is ≡ -1 (mod p).

And a proof is available at:
http://en.wikipedia.org/wiki/Wilson's_theorem
http://modular.fas.harvard.edu/edu/Fall2001/124/lectures/lecture6/html/node1.html
- and-
http://www.utm.edu/research/primes/notes/proofs/Wilsons.html
as well as at many other sources on the net (just look up "Wilson's Theorem").

I will refrain from duplicating these proofs here.

--- SK
Edited on October 16, 2003, 4:50 pm
  Posted by SilverKnight on 2003-10-16 11:23:06
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