Which number should come next at the end of this series 1, 4, 9, 16?

The next number in the series is 25.

This series is composed of perfect squares. The numbers you see are:

• 1 is 1 squared (1²)
• 4 is 2 squared (2²)
• 9 is 3 squared (3²)
• 16 is 4 squared (4²)

Continuing this pattern, the next number would be 5 squared (5²), which equals 25.