OFFSET
1,2
COMMENTS
A domino tower is a stack of bricks, where (1) each row is offset from the preceding row by half of a brick, (2) the bottom row is contiguous, and (3) each brick is supported from below by at least half of a brick.
The number of domino towers with n bricks is given by 3^(n-1).
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = (3^(n-1) + A320314(n))/2
EXAMPLE
For n=3, the a(3) = 6 domino towers are:
+-------+-------+-------+-------+
| | | | |
+-------+-------+-------+-------+
+-------+
| |
+---+---+---+---+
| | |
+-------+-------+
+-------+-------+
| | |
+---+---+---+---+
| |
+-------+
+-------+
| |
+-------+---+---+---+
| | |
+-------+-------+
+-------+
| |
+---+---+---+
| |
+---+---+---+
| |
+-------+
+-------+
| |
+---+---+---+
| |
+---+---+---+
| |
+-------+
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Kagey, Oct 10 2018
EXTENSIONS
Terms a(20) and beyond from Andrew Howroyd, Mar 12 2021
STATUS
approved