A145814 1/4 of the number of islands of ones fitting in an n X n array symmetric about both diagonal and antidiagonal with all ones connected only either three adjacent vertically or three adjacent horizontally.

0, 0, 0, 0, 1, 1, 1, 1, 3, 3, 4, 4, 6, 6, 7, 8, 10, 11, 12, 13, 15, 16, 19, 20, 22

Offset

1,9

Links

Table of n, a(n) for n=1..25.

Example

8 X 8 example with 4 islands
.0.0.0.0.1.0.0.0
.0.0.0.0.1.0.0.0
.0.0.0.0.1.0.0.0
.0.0.0.0.0.1.1.1
.1.1.1.0.0.0.0.0
.0.0.0.1.0.0.0.0
.0.0.0.1.0.0.0.0
.0.0.0.1.0.0.0.0

Crossrefs

Sequence in context: A025561 A342169 A187321 * A373797 A198465 A292836

Adjacent sequences: A145811 A145812 A145813 * A145815 A145816 A145817

Keyword

nonn

Author

R. H. Hardin, Oct 20 2008

Status

approved