Wilson Junior wants to determine the least positive integer such that . He applied Wilson's theorem as follows: We can see that the calculation of by setting parentheses in the starting steps is fallacious. So, what is the true, least positive value of
Notation:
denotes the
double factorial
notation. For example,
.
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Partial solution :
Note that N ≡ 8 2 ! ! ≡ 2 4 1 ⋅ 4 1 ! ( m o d 8 3 ) and 8 3 is prime, so in particular N 2 ≡ 2 8 2 ⋅ ( 4 1 ! ) 2 ( m o d 8 3 ) ≡ 1 ⋅ ( 4 1 ! ) 2 ( m o d 8 3 ) ≡ 4 1 ! ⋅ ( − 1 ) 4 1 ( − 1 ) ( − 2 ) ⋯ ( − 4 1 ) ≡ 4 1 ! ⋅ ( − 1 ) ⋅ ( 8 2 ) ( 8 1 ) ⋯ ( 4 2 ) ≡ ( − 1 ) ⋅ 8 2 ! ( m o d 8 3 ) ≡ ( − 1 ) ⋅ ( − 1 ) ( m o d 8 3 ) ≡ 1 ( m o d 8 3 ) by Fermat’s Little Theorem by Wilson’s theorem
Then using the fact 8 3 is prime once more, N 2 ≡ 1 ( m o d 8 3 ) ⇒ N ≡ ± 1 ( m o d 8 3 )
Therefore the only two possible answers are N = 1 or N = 8 2 . I don't know yet how to show N is not 1 (other than brute force).