Writing $a_n$ for a series

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Suppose if we have a pattern like this $$1=1^3$$ $$3+5=2^3$$ $$7+9+11=3^3$$ and so on.................

I want to know how do I write any $nth$ row in terms of $\sum$ notation?

MY work:

I have figured out that the first term of the each row is of the form $$n^2-n+1$$ and then every row is having a sequence with + 2 with preceding term till n value which can be written as $$\sum_{j=0}^{n-1} n^2 - n+1+2j$$

How to write summation for whole expression? ? Is it possible to write it in single summation ???

Can we write it using double summation also ? Expression the whole equation in summation notation both the sides

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The $n$-th row is then $$\sum_{k=0}^{n-1} (n^2-n+1+2k).$$