low and high. Count how many numbers from low to high inclusive have a number of positive divisors **other than** three (1 and the number itself both count as divisors).
Checking every number and its divisors will not do: the range can be almost a billion long.low=1, high=10 → 8
Only 4 (1, 2, 4) and 9 (1, 3, 9) have exactly three divisors. The other 8 numbers count.
low=20, high=30 → 10
Of the 11 numbers, only 25 (1, 5, 25) has exactly three divisors.
low=1, high=10
8
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