All graphs with at most three nodes are chordal, so a(n) = 1 for n <= 3 and any graph will be optimal (containing 1 maximal chordal subgraph).
For 4 <= n <= 9, the following graphs are optimal:
n = 4: the 4cycle;
n = 5: the 5cycle and the complete bipartite graph K_{2,3};
n = 6: the 3prism graph and the octahedral graph;
n = 7: the 3prism graph with one of the "long" edges subdivided by an additional node, and the complete graph with one triangle and two edges (pairwise nodedisjoint) removed;
n = 8: the gyrobifastigium graph;
n = 9: the Paley graph of order 9.
