Number of ways to build a contiguous building with n LEGO blocks of size 1 X 5 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.

A123793

Number of ways to build a contiguous building with n LEGO blocks of size 1 X 5 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) =3a(2) =5a(3) =18a(4) =42a(5) =170a(6) =405a(7) =1769a(8) =4507a(9) =20081a(10) =53008a(11) =240428a(12) =652160a(13) =3002052a(14) =8299727a(15) =38570944a(16) =108387118a(17) =507729121a(18) =1444491686a(19) =6809942459

External references