A Pre-RMO question! -2
How many two-digit positive integers are there having even numbers of divisors?
Note: numbers from to are not considered to be two digit numbers
The answer is 84.
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1 solution
First, let's observe one thing
So, we have basically remove all perfect squares from the set of integers from 10 to 99
Since there are 6 2-digit perfect squares, so there are a total of 9 0 − 6 = 8 4 numbers with even divisors