Which of the following numbers is
**
not
**
the product of a perfect square and a perfect cube?

972
961
980
968
900

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$972 = 6^{2} \times 3^{3}, 900 = 30^{2} \times 1^{3}, 968 = 11^{2} \times 2^{3}, 961 = 31^{2} \times 1^{3}$ .

On the other hand, $980 = 7^{2} \times 2^{2} \times 5$ cannot be written as the product of a perfect square and a perfect cube, as none of its divisors other than $1$ is a perfect cube and $980$ itself is not a perfect square.