\begin{tikzpicture}[
    squarednode/.style={rectangle, draw=black!20, fill=white!5, very thick, minimum size=1cm},
    ]
    
    \node[squarednode] at (0.5,0.5) (int) {1};
    \node[squarednode] at (1.5,0.5) (int) {2};
    \node[squarednode] at (2.5,0.5) (int) {4};
    \node[squarednode] at (3.5,0.5) (int) {7};
    \node[squarednode] at (0.5,1.5) (int) {3};
    \node[squarednode] at (1.5,1.5) (int) {5};
    \node[squarednode] at (0.5,2.5) (int) {6};
    \draw[very thick] (0,0)--(4,0)--(4,1)--(2,1)--(2,2)--(1,2)--(1,3)--(0,3)--cycle;
    
%    \node[squarednode] at (4.25,0.25) (int) {1};
%    \node[squarednode] at (4.75,0.25) (int) {2};
%    \node[squarednode] at (5.25,0.25) (int) {3};
%    \node[squarednode] at (5.75,0.25) (int) {5};
%    \node[squarednode] at (6.25,0.25) (int) {7};
%    \node[squarednode] at (4.25,0.75) (int) {4};
%    \node[squarednode] at (4.75,0.75) (int) {6};
%    \draw[step=0.5,gray, very thin] (4,0) grid (8,1.5);
%    \draw (4,1.5)--(8,0);
%    \draw[very thick] (4,0)--(6.5,0)--(6.5,0.5)--(5,0.5)--(5,1)--(4,1)--cycle;
    
    \end{tikzpicture}