77,040
If the fourth term were 2568 there is a simple answer, but with the series going up and down, I have no clue.
77040. It goes like, 107 * 2 = 214 214 * 3 = 642 642 * 4 = 2568, and so on. x * a(+1) = (a new)x Except that the word "completes" would suggest that there are no more terms. Not true!
77040
== ==
10,30,15,16,48,24,25
45
5
l
7
16
18
I