A145805 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 two adjacent vertically or two adjacent horizontally.

0, 0, 0, 1, 1, 1, 3, 3, 4, 6, 6, 7, 10, 10, 12, 15, 15, 17, 21, 21, 24, 28, 28, 31, 36, 36, 40, 45, 46, 50

Offset

1,7

Links

Table of n, a(n) for n=1..30.

Example

8 X 8 example with 12 islands:
  0 0 1 0 0 1 0 0
  0 0 1 0 0 1 0 0
  1 1 0 1 1 0 1 1
  0 0 1 0 0 1 0 0
  0 0 1 0 0 1 0 0
  1 1 0 1 1 0 1 1
  0 0 1 0 0 1 0 0
  0 0 1 0 0 1 0 0

Crossrefs

Sequence in context: A337019 A092200 A130481 * A277192 A098238 A088651

Adjacent sequences: A145802 A145803 A145804 * A145806 A145807 A145808

Keyword

nonn

Author

R. H. Hardin, Oct 19 2008

Status

approved