2. (6 points) Observe the pattern in the number table below, and we can know $x=$ $\qquad$
$$
\begin{array}{l}
1 \\
39 \\
\begin{array}{lll}
5 & 15 & 25
\end{array} \\
\begin{array}{llll}
7 & 21 & 35 & 49
\end{array} \\
9 \quad 27 \quad x \quad 63 \quad 81 \\
\begin{array}{llllll}
11 & 33 & 55 & 77 & 99 & 121
\end{array} \\
\end{array}
$$
【Answer】Solution: According to the analysis, $81=9^{2}$,

Therefore, $x=9 \times 5=45$; hence the answer is: 45 .