First differences are

4, 7, 10, 13, 16.

Second differences are all 3.

The Nth term will be given by

0 + (n-1)/1*(4 + (n-2)/2*(3))

where 0, 4, and 3 are the initial term of each of the series.

This can be written as

n(3n-1)/2 - 1

4, 7, 10, 13, 16.

Second differences are all 3.

The Nth term will be given by

0 + (n-1)/1*(4 + (n-2)/2*(3))

where 0, 4, and 3 are the initial term of each of the series.

This can be written as

n(3n-1)/2 - 1