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A123771
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Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1x3 which is symmetric after a rotation by 180 degrees.
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0
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1, 2, 12, 45, 264, 1128, 6991, 32202, 202856, 973242, 6204349
(list; graph; refs; listen; history; internal format)
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