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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 January 18 11:33 EST 2019. Contains 319271 sequences. (Running on oeis4.)