4, 9, 25 and 49
They are squares of prime numbers.
1 has one factor.
The numbers for which the sum of its proper factors is 1 less than the number is the powers of 2; less than 50 these are: 2, 4, 8, 16 & 32.
64.
30
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.
48 has 10 factors, the most factors of any number under 50.
48
42
1 has one factor.
The numbers for which the sum of its proper factors is 1 less than the number is the powers of 2; less than 50 these are: 2, 4, 8, 16 & 32.
64.
39
30
It is 30.
There is no such number. For if you considered 49.99 to be such a number, then 49.995 is a greater number and it is less than 50. And then 49.9955 is even greater and still less than 50. This process can go on without end.
36 The factors of 36 are : 36,18,12,9,6,4,3,2 and 1.
The number that is 50 less than 72 is 22