% \A, \Legend, \ymin, \ymax must be defined
% \def\A{0.6}
% \def\Legend{$0 < a < 1$}
% \def\ymin{0}
% \def\ymax{1}

\begin{tikzpicture} 
\begin{axis}[
axis lines*=middle,
enlargelimits = true,
ymin=\ymin,
ymax=\ymax,
xmin=-1,
xmax=5,
axis line style={->,>=stealth},
xlabel={\Large $n$},
ylabel={\Large $x[n]$},
yticklabel style = {yshift=0.2cm},
xticklabel style = {yshift=-0.1cm},
every axis x label/.style={
    at={(ticklabel* cs:1)},
    anchor=north,
},
every axis y label/.style={
    at={(ticklabel* cs:1)},
    anchor=south,
},
%xtick=\empty,
ytick={1},
xtick=\empty,
%xtick={-3.14, -1, 1, 3.14},
%xticklabels={$-\pi$, $-\omega_c$, $\omega_c$, $\pi$},
%xmajorgrids,
%ymajorgrids,
every outer y axis line/.append style={white!15!black},
every y tick label/.append style={font=\color{white!15!black}},
legend style={draw=white!15!black,fill=white,legend cell align=left}]

\addplot[ycomb, mark=*, fill=white, mark options={scale=1.5, fill=white}, line width=1.5pt, domain=0:5, samples=6] {pow(\A, x)};
\addplot[ycomb, mark=*, fill=white, mark options={scale=1.5, fill=white}, line width=1.5pt] 
table[row sep=crcr]{
	-1 0 \\
};
\node (alpha) at (axis cs: 2.5, 2) {\Large \tikz[baseline]{
		\node[fill=blue!20,anchor=base] (t1) {\Legend}}};
\end{axis}
\end{tikzpicture}
