  This paper studies the numbers of minimal generators of powers of monomial
ideals in polynomial rings. For a monomial ideal $I$ in two variables, Eliahou,
Herzog, and Saem gave a sharp lower bound $\mu (I^2)\ge 9$ for the number of
minimal generators of $I^2$ with $\mu(I)\geq 6$. Recently, Gasanova constructed
monomial ideals such that $\mu(I)>\mu(I^n)$ for any positive integer $n$. In
reference to them, we construct a certain class of monomial ideals such that
$\mu(I)>\mu(I^2)>\cdots >\mu(I^n)=(n+1)^2$ for any positive integer $n$, which
provides one of the most unexpected behaviors of the function $\mu(I^k)$. The
monomial ideals also give a peculiar example such that the Cohen-Macaulay type
(or the index of irreducibility) of $R/I^n$ descends.
