A^2=A\cdot A=\left[\left\{\begin{array}{ll}
0,&\hbox{za }m\not=n\\
\noalign{\smallskip}
m^2,&\hbox{za }m=n\end{array}\right.\right]_{m=1\atop n=1}^{\infty\atop\infty}=\left[\begin{array}{ccccccc}
1&0&0&0&0&0&\cdots\\
0&4&0&0&0&0&\cdots\\
0&0&9&0&0&0&\cdots\\
0&0&0&16&0&0&\cdots\\
0&0&0&0&25&0&\cdots\\
0&0&0&0&0&36&\cdots\\
\vdots&\vdots&\vdots&\vdots&\vdots&\vdots&\ddots\end{array}\right]