Number of ways to build a contiguous building with n LEGO blocks of size 1 X 2 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.

A123769

Number of ways to build a contiguous building with n LEGO blocks of size 1 X 2 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) =6a(4) =11a(5) =23a(6) =43a(7) =93a(8) =181a(9) =392a(10) =783a(11) =1710a(12) =3467a(13) =7623a(14) =15655a(15) =34543a(16) =71688a(17) =158721a(18) =332006a(19) =737213a(20) =1552365a(21) =3455004a(22) =7315948a(23) =16315297a(24) =34711474a(25) =77544359a(26) =165653643a(27) =370623055

External references