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A123771
Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 3 which is symmetric after a rotation by 180 degrees.
0
1, 2, 12, 45, 264, 1128, 6991, 32202, 202856, 973242, 6204349
OFFSET
1,2
LINKS
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Søren Eilers, Oct 29 2006
STATUS
approved