Find the number of positive integers 'm' such that (m-1)! is NOT exactly divisible by m excluding the prime values of 'm'.
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For positive non-primes m ≤ 4 , we have 1 ∣ ( 1 − 1 ) ! = 1 , 4 ∤ ( 4 − 1 ) ! = 6 . So the only such non-prime value ≤ 4 fulfilling the conditions in the question is 4 .
For non-primes m > 4 , we can express m as a product m = d 1 ∗ d 2 , where d 1 , d 2 are distinct proper factors of m (proper factors being factors of the number not equal to 1 or the number itself). We have d 1 , d 2 being factors of ( m − 1 ) ! , since d 1 , d 2 ≤ m − 1 and since the two are distinct, they are two non-repeating terms in the product ( m − 1 ) ! = 1 × 2 × ⋯ × ( m − 1 ) , hence we have m = d 1 ∗ d 2 ∣ ( m − 1 ) ! for all non-primes m > 4
In conclusion, the only non-primes m that satisfy this problem's conditions are m = 4 , consequently the number of such non-primes is 1