Explanation:
A
16 = 4×4 or 2×2×2×2
no triple factors.
so, this is wrong.
B.
42 = 7×6 = 7÷3÷2
no triple factors.
so, this is wrong.
C.
2197 = 13³ = 13×13×13 (a perfect cube).
that's it, there are no other factors possible, because 13 is a prime number.
so, they're cannot be suddenly 2 identical numbers that create 2197 out of their product.
so, this is wrong
D.
64 = 8×8 = 4×4×4 ÷ 2×2×2×2×2×2
this is true.
E.
121 = 11×11
abs that's it. again we are having prime numbers as factors. no more sub-factoring is possible.
but it did not matter. this reveals itself as perfect square.
this is true.