A145804 - OEIS

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A145804

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 two adjacent vertically or two adjacent horizontally.

0, 0, 1, 2, 2, 4, 6, 7, 9, 12, 13, 16, 20, 22, 25, 30, 32, 36

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

OFFSET

1,4

LINKS

Table of n, a(n) for n=1..18.

EXAMPLE

8 X 8 example with 14 islands

.0.1.1.0.0.0.1.1

.1.0.0.1.0.1.0.0

.1.0.0.1.0.1.0.1

.0.1.1.0.0.0.0.1

.0.0.0.0.0.1.1.0

.0.1.1.0.1.0.0.1

.1.0.0.0.1.0.0.1

.1.0.1.1.0.1.1.0

CROSSREFS

Sequence in context: A086536 A053045 A152424 * A227560 A046639 A178702

Adjacent sequences: A145801 A145802 A145803 * A145805 A145806 A145807

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 19 2008

STATUS

approved