*the second number 1,3,9,18,30,45 is the part where i can't find an expression that satisfies it*

First of all, it's:

0, 3, 9, 18, 30, 45...

Now, the series is: Difference is increasing by amount 3...

Series: 0, 3, 9, 18, 30, 45...

**Diff: 3(3-0), 6(9-3), 9(18-9), 12(30-18), 15(45-30)....**

I guess, now, this should be enough for you, to get this series equation. :)

UPDATE:

Here you go, the link that will explain how I got that: same series that I told you[^]

--SA