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jmc

number theory senior

Problem

Find the smallest positive integer with the following property: of the three numbers , , and , one of them is divisible by , one of them is divisible by , one is divisible by , and one is divisible by .
Solution
The most efficient means of searching for this trio of integers is to begin with the multiples of . The first such number is 49, which almost works, since 50 is divisible by and 48 is divisible by . But none of the nearby numbers is divisible by , so we move on to the next multiple of , which is 98. To our delight we discover that divides 99, while and divide 100. Hence we should take .
Final answer
98