  We look at the number $L(n)$ of $O$-sequences of length $n$. Recall that an
$O$-sequence can be defined algebraically as the Hilbert function of a standard
graded $k$-algebra, or combinatorially as the $f$-vector of a multicomplex. The
sequence $L(n)$ was first investigated in a recent paper by commutative
algebraists Enkosky and Stone, inspired by Huneke. In this note, we
significantly improve both of their upper and lower bounds, by means of a very
short partition-theoretic argument. In particular, it turns out that, for
suitable positive constants $c_1$ and $c_2$ and all $n>2$, $$e^{c_1\sqrt{n}}\le
L(n)\le e^{c_2\sqrt{n}\log n}.$$ It remains an open problem to determine an
exact asymptotic estimate for $L(n)$.
