|
|
A331878
|
|
Number of (non-null) connected induced subgraphs in a right-triangular graph with n vertices on each side.
|
|
1
|
|
|
1, 6, 32, 242, 3389, 94204, 5152184, 550554052, 114558123057, 46273463018266, 36187365370984792, 54676438562307219806, 159361336209506075254061, 894922393831489478287443136, 9673844907264825614989071514624, 201139020197000279384599867300494336
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
a(n) is the number of lower triangular n X n binary arrays with all 1's connected.
a(n) is the number of ways to place a fixed polyomino on an n X n grid with all squares above the main diagonal unoccupied.
|
|
LINKS
|
Eric Weisstein's World of Mathematics, Polyomino
|
|
EXAMPLE
|
The graphs for n = 2 and n = 3 are illustrated below:
o
o |
| o---o
o---o | |
o---o---o
.
The a(2) = 6 connected induced subgraphs are:
X o o X o X
o o X o o X X o X X X X
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|