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\documentclass[tikz, border=5pt]{standalone}

\newcommand{\xlen}{5mm}
\newcommand{\ylen}{4/5*\xlen}

\begin{document}
\begin{tikzpicture}[
    font=\sffamily,
    x=\xlen, y=\ylen,
    node size/.style={
        minimum width=\xlen, 
        minimum height=\ylen
    }
]
\foreach \x in {1,...,5}
    \foreach \y in {\x,...,5}
        \node [draw, node size] at (\x,-\y) (\x\y) {};

\foreach \rowColNum in {1,...,5}
    \path 
        (\rowColNum5) node [below=\ylen/2] {\rowColNum}
        (1\rowColNum) node [left=\xlen/2] {\the\numexpr\rowColNum+1}
    ;
\end{tikzpicture}
\end{document}

\documentclass[tikz, border=5pt]{standalone}

\newcommand{\xlen}{5mm}
\newcommand{\ylen}{4/5*\xlen}

\begin{document}
\begin{tikzpicture}[
    font=\sffamily,
    x=\xlen, y=\ylen,
    node size/.style={
        minimum width=\xlen, 
        minimum height=\ylen
    },
    conditional label/.code={
        \ifnum\x=1
            \pgfkeysalso{label=left:\the\numexpr\y+1}
        \fi
        \ifnum\y=5
            \pgfkeysalso{label=below:\x}
        \fi
    }
]
\foreach \x in {1,...,5}
    \foreach \y in {\x,...,5}
        \node [
            draw, 
            node size, 
            conditional label
        ] at (\x,-\y) (\x\y) {};
\end{tikzpicture}
\end{document}

\documentclass[border=5mm]{standalone}
\usepackage{array}
\begin{document}
\begin{tabular}{l*{5}{|m{.2cm}}|}
	\cline{2-2}
	2&\\\cline{2-3}
	3&&\\\cline{2-4}
	4&&&\\\cline{2-5}
	5&&&&\\\cline{2-6}
	6&&&&&\\\cline{2-6}
	\multicolumn{1}{c}{}&\multicolumn{1}{c}{1}&\multicolumn{1}{c}{2}&\multicolumn{1}{c}{3}&\multicolumn{1}{c}{4}&\multicolumn{1}{c}{5}\\
\end{tabular}
\end{document}