Question

121, 81, 49, 25,___ ?

Answer 1

121, 81, 49, 25, 9

================

Given sequence:

• 121, 81, 49, 25, ...

We can see it represents a sequence of perfect squares:

• 11², 9², 7², 5², ...

As each term is the square of an odd number in an descending order, we can assume the missing term is the square of three:

• 11², 9², 7², 5², 3²

So the missing number is 9.