a(3) is known to be 15 or 16. I have put 15 here because otherwise the sequence would be too short to include in the OEIS. But the true value is (or was in 1997 at least) not known.
L. W. Beineke, Biplanar graphs: a survey, Computers Math. Applic., 34 (1997), 1-8.
Table of n, a(n) for n=1..4.
Sequence in context: A076028 A281256 A070476 * A128662 A133192 A063684
Adjacent sequences: A124156 A124157 A124158 * A124160 A124161 A124162
N. J. A. Sloane, Dec 02 2006