It can be seen that the difference or subtraction between two successive terms of the sequence is always equal to 3.
11-8 = 3. 14-11 = 3. This means that the following term is always equal to the previous term plus three. Knowing this you can draw a formula or "rule" for succession. Assuming that the term 0 or X0 of the sequence is 8, then:
X (n) = 8 + 3n. So, the term 84 is: X (84) = 5 + 3 * (84). X (84) = 260. The series would be: ∑ 8 + 3x. from x=0 to x=59 The result of that sum is: 5790
