It is deficient: It's only proper divisors are 1, 3, and 7, which sums to 11, which is less than 21.
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Non-perfect square numbers are numbers that are not formed from the square of a number. 12, 13, 14, 21, 99, etc, are all non-perfect square numbers because when you square root them you do not get a whole number, which means they are not formed by any whole number, x, being squared (x^2).
Including 1, there are 21 perfect cubes between one and ten thousand. These are: 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000, 1331, 1728, 2197, 2744, 3375, 4096, 4913, 5832, 6859, 8000, 9261.
21 over 10 as a mixed number is 21/10
The divisors of 21 are: 1, 3, 7, 21.
the answer will be 21