Well I'm stuck on this question from past 2 hours.Idk what to do with it.I have this sequence and I have to find a formula for it.

1,3,7,13,21,31.....

I know that the difference between every 2 terms is 2,4,6,8

so the difference between the terms can be just another sequence like this

summation of (2i) where i = 1 to n.

I need some help with it.

Thanks