A number theory problem by Dhrubajyoti Ghosh

Find the greatest positive integer x x such that 2 3 x + 6 23^{x+6} divides 2000 ! 2000!


The answer is 83.

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1 solution

There are 86 86 multiples of 23 23 less than 2000 2000 .

However, 529 = 23 23 , 1058 = 23 23 2 , 1587 = 23 23 2 2 529=23\cdot23, 1058=23\cdot23\cdot2, 1587=23\cdot23\cdot2\cdot2 .

So there are total 89 89 23 23 's in 2000 ! 2000! .

So greatest positive integer x such that 2 3 x + 6 23^{x+6} divides 2000 ! 2000! can be found as follows:

x + 6 = 89 x+6=89

x = 83 \implies x=\boxed{83}

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