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Abstract for Helmut Prodinger,
Descendants in heap ordered trees or a triumph of computer algebra

 A  heap ordered tree with $n$ nodes (``size $n$'')
is a  planted plane tree
together with a bijection from the nodes to the set $\{1,\dots,n\}$
which is  monotonically increasing
 when going from the root to the leaves.
We consider the number of descendants  of the node $j$ in a (random)
heap ordered tree  of size $n\ge j$. 
 Precise expressions are derived for 
the probability distribution and all (factorial) moments.


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