Fill in 81, 54, 36, (), (), 32 / 3 according to the rule. What number should I fill in the blank?

Fill in 81, 54, 36, (), (), 32 / 3 according to the rule. What number should I fill in the blank?

81,54,36, (24), (16), 32 / 3
The former divided by 1.5 equals the latter