A211039 1/3 the number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors.

1, 9, 204, 12780, 2172082, 1005151346, 1266392434410, 4344083373089662, 40572956283401922254, 1031771738712216572967968, 71439807978713378989930266486, 13468111519258747911321811422788604

Offset

1,2

Links

Table of n, a(n) for n=1..12.

Example

Some solutions for n=4
..1..1..2..1....2..0..1..0....1..2..0..1....2..0..0..2....1..2..0..1
..1..1..2..1....0..2..2..2....2..2..1..2....0..2..0..0....2..1..0..2
..2..2..0..1....1..2..0..1....0..1..1..2....0..0..2..2....0..0..1..1
..1..1..1..1....0..2..1..1....1..2..2..2....2..0..2..2....1..2..1..2

Crossrefs

Sequence in context: A012108 A251587 A103914 * A307735 A266483 A203364

Adjacent sequences: A211036 A211037 A211038 * A211040 A211041 A211042

Keyword

nonn

Author

R. H. Hardin, Mar 30 2012

Status

approved