Number of ways to build a contiguous building with n LEGO blocks of size 1 X 4 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.

A123785

Number of ways to build a contiguous building with n LEGO blocks of size 1 X 4 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) =16a(4) =36a(5) =124a(6) =287a(7) =1043a(8) =2573a(9) =9448a(10) =24161a(11) =89827a(12) =235902a(13) =886047a(14) =2372494a(15) =8968829a(16) =24410414a(17) =92783928a(18) =255723571a(19) =976331352

External references