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[
^]