**There could be many answer for this series-**

I found it combination of two different series:

1st one: 4,6,12,30... & 2nd: 12,18,26...

1st sequence 4,6,12,30...

4*1.5=6

6*2=12

12*2.5=30

So next term would be 30*3=90

or

4+**2**=6

6+**6**(2*3)=12

12+**18**(6*3)=30

30+**54**(18*3)=84

2nd sequence 12,18,26...

12+6=18

18+8=26

So next term would be 26+10=36

Final series 4,12,6,18,12,26,30,36,90,48,315...

or

4,12,6,18,12,26,30,36,84.........