A123781 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 4 which is flat, i.e., with all blocks in parallel position and symmetric after a rotation by 180 degrees.

1, 1, 5, 7, 41, 65, 384, 649, 3853, 6745, 40209, 72334, 431188, 791144, 4717533, 8787824, 52396271, 98784645

Offset

1,3

Links

Table of n, a(n) for n=1..18.

Crossrefs

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

Sequence in context: A235365 A189241 A167205 * A120298 A178342 A117751

Adjacent sequences: A123778 A123779 A123780 * A123782 A123783 A123784

Keyword

nonn,more

Author

Søren Eilers, Oct 29 2006

Extensions

More terms by Søren Eilers, Sep 12 2018

Status

approved