10,20,30,40,50,60,70,80,90
Four numbers less than thirty, 12, 18, 20, and 28, each have exactly 6 factors.
There are 10 numbers less than 101 which have an odd number of factors: 1,4,9,16,25,36,49,64,81,100.
11
Prime numbers
The prime numbers less than 13 have the fewest factors. They are:235711
They all are prime numbers except 1
there are 3 no.2,3 & 5
14 (I think).
Just 36.
They are: 2 3 5 and 7 all of which are prime numbers
Perfect squares have an odd number of factors. There are 31 perfect squares less than 1000.