They are: 2 3 5 and 7 all of which are prime numbers
10,20,30,40,50,60,70,80,90
11
A whole number has an odd number of unique factors if and only if it is a perfect square. The perfect squares less than 10 are 0, 1, 4, and 9. Therefore, there are four whole numbers less than 10 that have an odd number of unique factors.
Prime numbers
Just 36.
14 (I think).
there are 3 no.2,3 & 5
Perfect squares have an odd number of factors. There are 31 perfect squares less than 1000.
They all are prime numbers except 1
Numbers with exactly 6 factors are perfect squares of prime numbers. The prime factorization of a number with exactly 6 factors is in the form ( p^2 ), where ( p ) is a prime number. There are 10 prime numbers less than 30: 2, 3, 5, 7, 11, 13, 17, 19, 23, and 29. So, there are 10 numbers less than 30 that have exactly 6 factors.
All but the square numbers - 53 of them.
There are a few numbers that are less than 19 and have more than 4 factors. The number 10 is less than 19 and has more than four factors.