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One hundred is the least three-digit square number. It is formed by 102.
198 is the greatest three-digit even number that has no factor equal to 4.
36
144, 324, 576 and 900 are even three-digit square numbers that are multiples of 3.
102 = 100 which is the first possible three digit number that is a perfect square. 312 = 961 which is the last possible three digit number that is a perfect square. So there are 22 three digit positive numbers that are perfect squares.
100
999
121
"Taking a cube" is the same basic procedure, whether it's a one-digit number, a three digit number, a complex number, a square matrix, or anything else you can multiply. Taking the cube simply means, multiply the number by itself, in such a way that it appears three times as a factor. For example, if your three-digit number is 235, you calculate the cube as 235 x 235 x 235.
998
102
Anything three-digit would have to be a multiple, like 280.