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A145806 1/4 of the number of islands of ones fitting in an n X n array symmetric under 90-degree rotation with all ones connected only either two adjacent vertically or two adjacent horizontally. 0
0, 0, 0, 1, 1, 2, 3, 3, 4, 6, 6, 8, 10, 11, 12, 15, 16, 18, 21, 23, 25 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..21.

EXAMPLE

8 X 8 example with 12 islands:

  0 0 0 1 0 0 1 0

  1 1 0 1 0 0 1 0

  0 0 1 0 1 1 0 0

  0 0 1 0 0 0 1 1

  1 1 0 0 0 1 0 0

  0 0 1 1 0 1 0 0

  0 1 0 0 1 0 1 1

  0 1 0 0 1 0 0 0

CROSSREFS

Sequence in context: A118096 A296440 A181692 * A100989 A188215 A162627

Adjacent sequences:  A145803 A145804 A145805 * A145807 A145808 A145809

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 19 2008

STATUS

approved

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Last modified June 18 20:04 EDT 2021. Contains 345121 sequences. (Running on oeis4.)