A235281 Number of (n+1) X (n+1) 0..3 arrays with every 2 X 2 subblock having its diagonal sum differing from its antidiagonal sum by 4 (constant-stress 1 X 1 tilings).

20, 68, 148, 380, 740, 1724, 3220, 7196, 13220, 28988, 52948, 115100, 210020, 454844, 830740, 1796636, 3286820

Offset

1,1

Links

Table of n, a(n) for n=1..17.

Formula

Empirical: a(n) = a(n-1) +9*a(n-2) -9*a(n-3) -26*a(n-4) +26*a(n-5) +24*a(n-6) -24*a(n-7).

Example

Some solutions for n=4:
  2 0 3 0 1     1 3 1 3 2     2 0 2 1 2     0 2 1 2 0
  1 3 2 3 0     2 0 2 0 3     0 2 0 3 0     2 0 3 0 2
  2 0 3 0 1     0 2 0 2 1     3 1 3 2 3     1 3 2 3 1
  1 3 2 3 0     2 0 2 0 3     0 2 0 3 0     2 0 3 0 2
  2 0 3 0 1     0 2 0 2 1     3 1 3 2 3     0 2 1 2 0

Crossrefs

Diagonal of A235289.

Sequence in context: A304253 A330931 A158444 * A303620 A221521 A145191

Adjacent sequences: A235278 A235279 A235280 * A235282 A235283 A235284

Keyword

nonn

Author

R. H. Hardin, Jan 05 2014

Status

approved