\documentclass[12pt]{article}
\usepackage[greek,english]{babel}
\usepackage{amsmath}
\begin{document}
A=~
$\begin{bmatrix}
a_{11} & a_{12} & \cdots & a_{1n}\\
a{21} & a_{22} & \cdots & a_{2n}\\
\vdots & \vdots & \ddots & \vdots\\
a_{m1} & a_{m2} & \cdots & a_{mn}
\end{bmatrix}$
\begin{equation}
p(n)=~ \sum_{m=2}^{n}[\sum_{k=1}^{m-1}\frac{m/k}{{m/k}^{-1}}]
\end{equation}
$\begin{Bmatrix}
a = f(z)\\
b = f(z^{2})\\
j = f(z^{3})
\end{Bmatrix}$
\begin{equation}
p_{1}(n)=\varinjlim_{m \infty}\sum_{n=1}^{\infty}(1-cos^{2m}(n!^{n}p/n))
\end{equation}
\begin{equation}
\prod_{j\geq 0}~\begin{pmatrix}\sum_{k\geq o}a_{jk}z^{k}\end{pmatrix}~=\sum_{{n>0}_{k>0}}z^{n}
\end{equation}
\begin{equation}
\sqrt{1 +{\sqrt{1 + {\sqrt{1 +{\sqrt{1+x}}}}}}}
\end{equation}
\begin{equation}
\iint_{0}^{a=n}xdx
\end{equation}
\end{document}

