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, 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

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 A327637 A366409

Adjacent sequences: A145812 A145813 A145814 * A145816 A145817 A145818

Keyword

nonn

Author

R. H. Hardin, Oct 20 2008

Status

approved