What number comes next in following series 9,12,21,48

问题描述:

What number comes next in following series 9,12,21,48

前一项减去5,再乘以3,得到后一项
12=(9-5)×3
21=(12-5)×3
48=(21-5)×3
那么接下来就是(48-5)×3=129