There is only 1, the number 54.
There are none.
49
666 integers.
There are 44 positive integers less than 2,010 that have an odd number of factors.
52
10*9*8=720
There are 20.
There is only 1, the number 54.
There are 870 such numbers.
125
Three of them.
3
There are none.
20. 16 without repeating a digit.
49
666 integers.