  Take ${\sf Q}=({\sf Q}_1,{\sf Q}_2,\ldots)$ to be an exponential structure
and $M(n)$ to be the number of minimal elements of ${\sf Q}_n$ where $M(0)=1$.
Then a sequence of numbers $\{r_n({\sf Q}_n)\}_{n\ge 1}$ is defined by the
equation \begin{eqnarray*} \sum_{n\ge 1}r_n({\sf
Q}_n)\frac{z^n}{n!\,M(n)}=-\log(\sum_{n\ge 0}(-1)^n\frac{z^n}{n!\,M(n)}).
\end{eqnarray*} Let $\bar{{\sf Q}}_n$ denote the poset ${\sf Q}_n$ with a
$\hat{0}$ adjoined and let $\hat{1}$ denote the unique maximal element in the
poset ${\sf Q}_n$. Furthermore, let $\mu_{{\sf Q}_n}$ be the M\"{o}bius
function on the poset $\bar{{\sf Q}}_n$. Stanley proved that $r_n({\sf
Q}_n)=(-1)^n\mu_{{\sf Q}_n}(\hat{0},\hat{1})$. This implies that the numbers
$r_n({\sf Q}_n)$ are integers. In this paper, we study the cases ${\sf
Q}_n=\Pi_n^{(r)}$ and ${\sf Q}_n={\sf Q}_n^{(r)}$ where $\Pi_n^{(r)}$ and ${\sf
Q}_n^{(r)}$ are posets, respectively, of set partitions of $[rn]$ whose block
sizes are divisible by $r$ and of $r$-partitions of $[n]$. In both cases we
prove that $r_n(\Pi_n^{(r)})$ and $r_n({\sf Q}_n^{(r)})$ enumerate the pyramids
by applying the Cartier-Foata monoid identity and further prove that
$r_n(\Pi_n^{(r)})$ is the generalized Euler number $E_{rn-1}$ and that
$r_n({\sf Q}_n^{(2)})$ is the number of complete non-ambiguous trees of size
$2n-1$ by bijections. This gives a new proof of Welker's theorem that
$r_n(\Pi_n^{(r)})=E_{rn-1}$ and implies the construction of $r$-dimensional
complete non-ambiguous trees. As a bonus of applying the theory of heaps, we
establish a bijection between the set of complete non-ambiguous forests and the
set of pairs of permutations with no common rise. This answers an open question
raised by Aval {\it et al.}.
