login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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. 0
1, 3, 5, 16, 36, 124, 287, 1043, 2573, 9448, 24161, 89827, 235902, 886047, 2372494, 8968829, 24410414, 92783928, 255723571, 976331352 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The base block is not counted among the n and must be the only block in the bottom layer of the building.

LINKS

Table of n, a(n) for n=1..20.

CROSSREFS

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

Sequence in context: A295358 A077551 A106588 * A121646 A226205 A300533

Adjacent sequences:  A123782 A123783 A123784 * A123786 A123787 A123788

KEYWORD

nonn

AUTHOR

Søren Eilers, Oct 29 2006

EXTENSIONS

a(14)-a(20) from Søren Eilers, Sep 16 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 26 03:40 EDT 2022. Contains 356986 sequences. (Running on oeis4.)