Let $(a_0,a_1,\dots, a_n)$ be a sequence of non-negative integers.

Q. When does there exists a graph $G$ such that its number of $k$-cliques is $a_k$ (that is $G$ has $a_0$ vertices, $a_1$ edges, $a_2$ trinagles, etc)?

Probably, it is hopeless to get a complete description of such sequences, so I am interested in any necessary or sufficient conditions on $\{a_i\}$.