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A145815 1/4 of the number of islands of ones fitting in an n X n array symmetric about the diagonal and under 90 degree rotation with all ones connected only either three adjacent vertically or three adjacent horizontally. 0
0, 0, 0, 0, 1, 0, 1, 0, 3, 2, 4, 4, 6, 4, 7, 6, 10, 8, 12, 12, 15, 14, 19, 16, 22, 20, 26, 24, 31, 28 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,9

LINKS

Table of n, a(n) for n=1..30.

EXAMPLE

9 X 9 example with 12 islands

.0.1.1.1.0.1.1.1.0

.1.0.0.0.0.0.0.0.1

.1.0.0.1.1.1.0.0.1

.1.0.1.0.0.0.1.0.1

.0.0.1.0.0.0.1.0.0

.1.0.1.0.0.0.1.0.1

.1.0.0.1.1.1.0.0.1

.1.0.0.0.0.0.0.0.1

.0.1.1.1.0.1.1.1.0

CROSSREFS

Sequence in context: A154392 A069745 A112199 * A059851 A047993 A033177

Adjacent sequences:  A145812 A145813 A145814 * A145816 A145817 A145818

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 20 2008

STATUS

approved

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Last modified October 21 06:44 EDT 2018. Contains 316405 sequences. (Running on oeis4.)