Mary has a sequence , such that for each is the least positive integer for which none of the base- logarithms are integers. Find the largest number in her sequence.
Solution
It is not difficult to see that for all of the logarithms to be non-integers, they must lie strictly between and for some integer . Therefore, we require , and so where is the smallest integer that satisfies the inequality. In particular, this means that . Note that since and (since ). we now show that 2188 is the maximum possible value for . If , then . If , then and thus . If , then , which gives , and thus . If , then , which gives , and thus . If , then , which gives , and thus . It then remains to check the value of and . Indeed, and , so no values of exceeds 2188.
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