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, 1, 1, 2, 3, 3, 4, 6, 6, 8, 10, 11, 12, 15, 16, 18, 21, 23, 25

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