Number of ways to build a contiguous building with n LEGO blocks of size 1 X 3 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.
A123777
Number of ways to build a contiguous building with n LEGO blocks of size 1 X 3 on top of a fixed block of the same size so that the building is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.
Terms
- a(0) =1a(1) =2a(2) =3a(3) =7a(4) =14a(5) =37a(6) =76a(7) =217a(8) =473a(9) =1374a(10) =3104a(11) =9196a(12) =21240a(13) =63929a(14) =150294a(15) =456703a(16) =1089683a(17) =3338624a(18) =8055267a(19) =24845592a(20) =60511113a(21) =187665038a(22) =460638240
External references
- oeis: A123777