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.
By definition, a prime number has exactly two factors. So, there are no prime numbers with exactly three factors.
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.
4, 9, 25 and 49 They are squares of prime numbers.
11
Just 36.
there are 3 no.2,3 & 5
14 (I think).
1, 2, 3, 5, and 7
Every prime number has exactly two factors. They are '1' and the number itself. There are 15 prime numbers less than 50. A few of them are 2, 3, 5, 7, 11, 13, and 47.
4, 9, 25, and 49
4, 9, 25, 49
Nothing special. They are squares of prime numbers.