5. (5 points) There are some natural numbers (excluding 0) that are both square numbers and cube numbers. (Note: A square number can be written as the product of two identical natural numbers, and a cube number can be written as the product of three identical natural numbers). For example: $1=1 \times 1=1 \times 1 \times 1 \quad 64$ $=8 \times 8=4 \times 4 \times 4$. Therefore, among the natural numbers less than 1000, there are $\qquad$ such numbers.
【Answer】Solution: A number that is both a square and a cube must be a perfect sixth power, so: $1^{6}=1, 2^{6}=64, 3^{6}=729, 4^{6}=4096 \cdots$ and $4^{6}=4096$ exceeds 1000, so there are 3 in total. Therefore, the answer is: 3.