What is the English term for "cellular triangular matrix " i.e. a matrix like e.g.
$$ \begin{bmatrix} 1 & 2& 4 & & & & & \\ 2 & 3& 5 & & & & & \\ 7 & 8& 1 & & & & & \\ &&&7&&&&\\ &&&&4&5&&\\ &&&&2&1&&\\ &&&&&&8&9\\ &&&&&&2&6 \end{bmatrix} $$
All the other elements are zeros.
What happens when we raise it to some power n? I think effectively the smaller matrices along the main diagonal are raised to power n.
I need the English term so that I can look up some more information about these matrices and their properties.