I am have $n$ vertices and trying to enumerate all possible DAGs $\theta$ over $n$. How many DAGs are there? For example when $n=2$, there are 3 possible DAGs and when $n=3$ I tried the following:
$|E|=0$, $|\theta|=1$
$|E|=1$, $|\theta|=6$
$|E|=2, |\theta|=8$
$|E|=3,|\theta|=3$
what is the general formula for counting the number of DAGs with $n$ vertices?