4. Arrange the positive odd numbers as shown in Figure 2, and denote the element in the $i$-th row and $j$-th column as $a_{4}$.
(1) Find the sum of all $a_{\eta}$ that satisfy $i+j=n+1\left(n \in \mathbf{N}_{+}\right)$;
(2) Find the sum of all $a_{4}$ that satisfy $i+j \leqslant n+1\left(n \in \mathbf{N}_{+}\right)$;
(3) If $a_{i}=2005$, find $i$ and $j$.
(1) $n^{3}$
(2) $\left[\frac{n(n+1)}{2}\right]^{2}$
(3) $i=13 \quad j$ = 33)