Find the missing number of the series: 8, 78, 318, 720, ?, 2010

Question

What is the next number of the following series: 8, 78, 318, 720, ?
Also tell the relation between 8,78

Answer 1

3^2 - 1 = 8
9^2 - 3 = 78
18^2 - 6 = 318
27^2 - 9 = 720
36^2 - 12 = 1284
45^2 - 15 = 2010

therefore answer is 1284

Answer 2

8 = (3*1)^2-1
78 = (3*3)^2-3
318 = (3*6)^2-6
720 = (3*9)^2-9
1284 = (3*12)^2-12
2010 = (3*15)^2-15

Answer is 1284