A145813 - OEIS

A145813

1/2 the number of islands of ones fitting in an n X n array symmetric about main diagonal with all ones connected only either three adjacent vertically or three adjacent horizontally.

0, 0, 0, 1, 2, 2, 3, 4, 6, 7, 8, 10, 12, 14, 16, 19, 21, 24, 27, 30

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,5

LINKS

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

EXAMPLE

8 X 8 example with 8 islands

.0.0.0.0.0.0.0.1

.0.0.0.1.1.1.0.1

.0.0.0.0.0.0.0.1

.0.1.0.0.1.1.1.0

.0.1.0.1.0.0.0.1

.0.0.0.1.0.0.0.1

.1.1.1.0.1.1.1.0

CROSSREFS

Sequence in context: A370778 A075465 A011868 * A240865 A039859 A130291

Adjacent sequences: A145810 A145811 A145812 * A145814 A145815 A145816

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 20 2008

STATUS

approved