Enumerates a subclass of the things counted by A004003.
"Fault-free" means that every straight line through the interior of the square hits the interior of some domino.
Xu Mingkuan, Table of n, a(n) for n = 1..12
Sequence in context: A251227 A183648 A242141 * A031837 A237865 A202646
Adjacent sequences: A124994 A124995 A124996 * A124998 A124999 A125000
Don Knuth, Jun 26 2008
a(7) from Alois P. Heinz, Oct 19 2015
a(8)-a(11) from Xu Mingkuan, Dec 23 2016