---

for k = [4, 5, 6]
    a = zeros(k, k);
    for m = 1:k
        for n = 1:k
            if m == n
                a(m,n) = 2;
            elseif abs(m-n) == 2
                a(m,n) = 1;
            else
                a(m,n) = 0;
            end
        end
    end
    fprintf('\nk = %d, matrix a =\n', k);
    disp(a)
end