Wednesday, 8 July 2015

Factorial Divisors

Q. For what maximum value of n will the expression 10200!504n be an integer? I have the solution to this question and I would like you to please go through the solution below. My doubt follows the solution :)



The solution can be found by writing 504=23327 and then finding the number of 23s, 32s and 7s in the numerator, which can be obtained by



Number of 2s = 102002+1020022+1020023++10200213=10192
where is the floor function.




Therefore, the number of 23s=101923=3397



Similarly, the number of 32s=2457and the number of 7s=1698



The number of factors of 23327 is clearly constrained by the number of 7s, therefore n=1698.



My question is, whether there is any way I can simply look at the prime factors of the divisor and know which prime factor is going to be the constraining factor? (as 7 was, in this particular example)

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