what is the pattern of 4,6,9,13.5

Question

1. each number is 0.5 times the previous number
2. each number is 1.5 times the previous number
3. each number is 2/3 of the next number 
4. each number is 3/2 of the previous number

Answer 1

Actually each number is 1.5 and 3/2 times the previous number.