Formula for the sequence 0,3,8,15,24 ... Out of my own interest I've been practicing finding formula for for sequences and I've been having trouble finding one for the nth term for this sequence.
0,3,8,15,24 ... 
Clearly you add 5,7,9,11 ... to the previous number but if anyone had some insight about how to express this in a formula that would be much appreciated.

A recursive general formula seems to be
$$
n_0 = 0
$$
$$
n_k = n_{k-1} + 2k+1
$$
