OFFSET
1,4
EXAMPLE
For n=3, we have 2 fixed polyominoes in equilibrium: namely the vertical 3-omino and the horizontal 3-omino, thus a(3)=2.
CROSSREFS
KEYWORD
hard,more,nonn
AUTHOR
Mark Elduck (mark.elduck(AT)gmail.com), Dec 12 2009, Dec 20 2009, Dec 21 2009
STATUS
approved