How many graphs are unions of <i>k</i>-cliques?

Béla Bollobás Graham Brightwell How many graphs are unions of <i>k</i>-cliques? 87-107 2006 52 Journal of Graph Theory 2 http://dx.doi.org/10.1002/jgt.20138 db/journals/jgt/jgt52.html#BollobasB06