What is the pattern rule for 1-1-2-3-5-8-13-21-34 pattern?

Answer 1

This is the famous fibonacci sequence, where each term in the sequence is the sum of the previous two.

Fn=Fn-1 + Fn-2

F0 = 1 and F1 = 1 are the initial values to begin the sequence.

F2 = F1 + F0 = 1 + 1 = 2

F3 = F2 + F1 = 2 + 1 = 3

and so on