9 = 1, 3, 9
4 = 1, 2, 4
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11
4, 9, 25, 49
6 (1,2,3,6) 10 (1,2,5,10) and 15 (1,3,5,15).
The numbers less than 100 with exactly 6 factors are of the form a2b where a and b are different primes. 12, 18, 20, 28, 44, 45, 50, 52, 63, 68, 75, 76, 92 and 99.
There are 31 numbers less than 1,000 which have an odd number of factors. They are: 1,4,9,16,25,36,49,64,81,100,121,144,169,196,225,256,289,324,361,400,441,484,529,576,625,676,729,784,841,900,961.