2 3 5 8 12 17 what is the rule among these number?

Answer 1

Each number in the series is the sum of the previous number and one less than its numerical position in the series.

How it works in this problem:

To get from 2 to 3, add 1

To get from 3 to 5, add 2

To get from 5 to 8, add 3

To get from 8 to 12, add 4

etc.