If an=an−1+2na_n = a_{n-1} + 2nan=an−1+2n and a0=0a_0 = 0a0=0, what is the sum representation of ana_nan?
an=∑i=1nia_n = \sum_{i=1}^{n} ian=∑i=1ni
an=2∑i=1nia_n = 2 \sum_{i=1}^{n} ian=2∑i=1ni
an=∑i=1ni2a_n = \sum_{i=1}^{n} i^2an=∑i=1ni2
an=n∑i=1n1a_n = n \sum_{i=1}^{n} 1an=n∑i=1n1