A145807 1/2 the number of islands of ones fitting in an n X n array symmetric under 180 degree rotation with all ones connected only either two adjacent vertically or two adjacent horizontally.

0, 0, 1, 2, 3, 4, 6, 8, 9, 12, 14, 18, 20, 23, 27, 32

Offset

1,4

Links

Table of n, a(n) for n=1..16.

Example

8 X 8 example with 16 islands
.0.1.0.1.0.1.0.1
.0.1.0.1.0.1.0.1
.1.0.1.0.1.0.1.0
.1.0.1.0.1.0.1.0
.0.1.0.1.0.1.0.1
.0.1.0.1.0.1.0.1
.1.0.1.0.1.0.1.0
.1.0.1.0.1.0.1.0

Crossrefs

Sequence in context: A036407 A374243 A376154 * A278962 A122380 A033501

Adjacent sequences: A145804 A145805 A145806 * A145808 A145809 A145810

Keyword

nonn

Author

R. H. Hardin, Oct 19 2008

Status

approved