whats the missing number

Question

....81,64,49,36,25,16

Answer 1

The missing number is 9.

The numbers are decreasing by 3 each time:
81, 81-3=78, 78-3=75, 75-3=72, 72-3=69, 69-3=66, 66-3=63, 63-3=60, 60-3=57, 57-3=54, 54-3=51, 51-3=48, 48-3=45, 45-3=42, 42-3=39, 39-3=36, 36-3=33, 33-3=30, 30-3=27, 27-3=24, 24-3=21, 21-3=18, 18-3=15, 15-3=12, 12-3=9, 9-3=6, 6-3=3, 3-3=0.

Answer 2

the next number is 9, but not for the reason you showed.
the differences decrease by 2 each time. The sequence is
... 81-17=64-15=49-13=36-11=25-9=16-7=9

Answer 3

Apologies for the oversight in my previous response. Thank you for correcting that.

The pattern in this sequence is correct in the differences decreasing by 2 each time. The missing number should indeed be 9.

Thank you for pointing out the error, and I appreciate the clarification.