MathDB

The board was placed

\begin{array}{rcl}<br /> 1 & = & 1 \\<br /> 2 + 3 + 4 & = & 1 + 8 \\<br /> 5 + 6 + 7 + 8 + 9 & = & 8 + 27\\<br /> 10 + 11 + 12 + 13 + 14 + 15 + 16 & = & 27 + 64\\<br /> & \ldots &<br /> \end{array}

Write such a formula for the

n

-th row of the array that, with the substitutions

n = 1, 2, 3, 4

, would give the above four lines of the array and would be true for every natural

n

2