A210928 - OEIS

A210928

Number of n X n 0..3 symmetric matrices with every element equal to zero or one horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order.

1, 2, 55, 5892, 2081181, 2353015360, 8533282805517, 99227545384370981, 3699909251614783425693, 442375363534050667939662012, 169602369911112134429648742314656

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..11.

EXAMPLE

Some solutions for n=4

..0..1..2..0....0..1..3..0....0..1..1..2....0..1..2..1....0..1..3..3

..1..2..1..3....1..2..0..2....1..2..3..1....1..0..3..3....1..2..0..0

..2..1..2..3....3..0..1..2....1..3..1..2....2..3..2..1....3..0..3..2

..0..3..3..2....0..2..2..0....2..1..2..3....1..3..1..0....3..0..2..0

CROSSREFS