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Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 3 which is flat, i.e., with all blocks in parallel position.
0

%I #7 Jul 21 2017 15:35:51

%S 1,3,17,107,761,5607,42730,331851,2618024,20895964,168398683,

%T 1367838390,11184711448,91976811135

%N Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 3 which is flat, i.e., with all blocks in parallel position.

%Y Cf. A112389, A123762 - A123827, A123829 - A123849.

%K nonn,hard

%O 1,2

%A _Søren Eilers_, Oct 29 2006