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.........
