Which one of these numbers is not like the others? \( 25,16,49,63,81 \)

The number \( 63 \) stands out from the rest because it is not a perfect square. The numbers \( 25 \) (5²), \( 16 \) (4²), \( 49 \) (7²), and \( 81 \) (9²) are all perfect squares, while \( 63 \) does not fit into that group and is instead a product of \( 3 \times 21 \). In puzzles like this, look for patterns such as even vs. odd, prime numbers, or properties like being a square or cube. Grouping similar characteristics can make it easier to spot the odd one out. Remember, sometimes the answer can be a simple but overlooked property!