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49 has three factors: 1, 7, 49
A composite number is a number that is not a prime number, ie it has more than two distinct factors. The factors of 25 are 1, 5, 25 - three distinct factors.
878 three digit numbers have an even number of factors. Every factor of a number has a pair, so there ought to be an even number of factors for every number. However, if a pair of the factors are the same number, then there will be an odd number of factors, that is if the number is a perfect square. Assuming three digit numbers are 100 to 999: From 100 to 999, the perfect squares are 102 = 100 to 312 = 961, a total of 31-10+1 = 22 numbers. So of the 999-100+1 = 900 three digit numbers, 22 have an odd number of factors, so 900-22 = 878 have an even number of factors.
A number is called a staircase composite number when it has three prime factors that have different sized digits: the first is one digit, the second is two digits and the third is three digits. For example: [7] [41] [271] x 77 777 77 777 would be the staircase composite number.
The square root of a number is the inverse of the square. For example, three squared equals nine, so the square root of nine is equal to three.