Remark
This looks like an arithmetic series. If it is you should be able to show that the difference is a constant. It is shown like this
a_n - a_(n -1) = k
a2 - a1 = 10 - 2 = 8
a3 - a2 = 18 - 10 = 8
Conclusion It looks like we do have an arithmetic series.
100th number
a = 2
d = 8
n = 100
a_100 = ?
Formula
a_n = a + (n - 1)d
Solve
a_100 = 2 + (100 - 1) * 8
a_100 = 2 + 99*8
a_100 = 2 + 792
a_100 = 794