Biconnected means "at least 2-connected". The corresponding sequence for 3-connected bipartite planar graph is A007028, where the term "polyhedral graph" is used as shorthand for "3-connected planar graph".

a(4) = 1 because the 4-cycle is the only planar and bipartite graph on 4 vertices that is at least 2-connected and a(5) = 1 because the complete bipartite graph K2,3 is the only such graph on 5 vertices.