Any graph can be broken up into 2 subgraphs, one of which is Konig-Egervary (KE) and the other of which has the property that non-empty independent sets have more neighbors. Following a conjecture of Fajtlowicz, Carl Yerger has shown that almost all graphs have an empty KE part. Many very small graphs have a non-empty KE part. These graphs are “reducible”: calculating the independence number for them efficiently reduces to the problem of calculating the independence number of a proper subgraph. Here’s the data:

there are 11 graphs with 4 vertices

there are 10 graphs with non-empty KE component

there are 34 graphs with 5 vertices

there are 25 graphs with non-empty KE component

there are 156 graphs with 6 vertices

there are 124 graphs with non-empty KE component

there are 1044 graphs with 7 vertices

there are 616 graphs with non-empty KE component

there are 12346 graphs with 8 vertices

there are 7065 graphs with non-empty KE component

there are 274668 graphs with 9 vertices

there are 90034 graphs with non-empty KE component