In this sequence there are actually two sequences. 1 sequence for the numerators and one sequence for the denominators. The following transformation applies to the sequence for the denominators : +3
This creates the following sequence: [1, 4, 7, 10, 13]
The following transformation applies to the sequence for the numerators: +1
This creates the following sequence: [13, 14, 15, 16, 17]
Take a good look at how to rewrite the fractions in the series to recognize the pattern.
For example, 2/7 can be rewritten as 4/14