A145816 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 three adjacent vertically or three adjacent horizontally.

0, 0, 0, 0, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 9, 9, 11, 12, 14, 15, 17, 18

Offset

1,7

Links

Table of n, a(n) for n=1..22.

Example

8 X 8 example with 8 islands:
  1 0 0 1 0 1 1 1
  1 0 0 1 0 0 0 0
  1 0 0 1 0 0 0 0
  0 0 0 0 0 1 1 1
  1 1 1 0 0 0 0 0
  0 0 0 0 1 0 0 1
  0 0 0 0 1 0 0 1
  1 1 1 0 1 0 0 1

Crossrefs

Sequence in context: A300788 A120171 A364915 * A347610 A027583 A029022

Adjacent sequences: A145813 A145814 A145815 * A145817 A145818 A145819

Keyword

nonn

Author

R. H. Hardin, Oct 20 2008

Status

approved