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jmc

number theory senior

Problem

A subset of the integers has the property that none of its members is 3 times another. What is the largest number of members such a subset can have?
Solution
Notice that inclusion of the integers from to is allowed as long as no integer between and inclusive is within the set. This provides a total of = 67 solutions. Further analyzation of the remaining integers between and , we notice that we can include all the numbers except (as including would force us to remove both and ) to obtain the maximum number of solutions. Thus, .
Final answer
76