A123805 Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 7 which is flat, i.e., with all blocks in parallel position, and symmetric after a rotation by 180 degrees.

1, 1, 7, 10, 100, 160, 1688, 2853, 30903, 53721, 592395, 1053025, 11711448, 21151575, 236789391, 432872895

Offset

1,3

Links

Table of n, a(n) for n=1..16.

Crossrefs

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

Sequence in context: A350533 A351685 A123797 * A124200 A282038 A133346

Adjacent sequences: A123802 A123803 A123804 * A123806 A123807 A123808

Keyword

nonn

Author

Søren Eilers, Oct 29 2006

Extensions

a(11)-a(16) from Søren Eilers, Sep 14 2018

Status

approved