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A230701
Number of (n+3) X (1+3) 0..2 white square subarrays x(i,j) with each element diagonally or antidiagonally next to at least one element with value (x(i,j)+1) mod 3, and upper left element zero.
2
2, 8, 30, 102, 348, 1172, 3956, 13326, 44916, 151338, 509978, 1718408, 5790456, 19511640, 65747178, 221543696, 746521190, 2515502046, 8476319172, 28562083692, 96243740012, 324306077270, 1092792451740, 3682309466130, 12408031373682
OFFSET
1,1
COMMENTS
Column 1 of A230708.
LINKS
FORMULA
Empirical: a(n) = 3*a(n-1) + 3*a(n-2) - 6*a(n-3) + a(n-5).
Empirical g.f.: 2*x*(1 + x) / ((1 - x)*(1 - 2*x - 5*x^2 + x^3 + x^4)). - Colin Barker, Mar 17 2018
EXAMPLE
Some solutions for n=2:
..0..x..0..x....0..x..1..x....0..x..0..x....0..x..0..x....0..x..2..x
..x..1..x..1....x..1..x..2....x..1..x..2....x..1..x..2....x..1..x..0
..0..x..2..x....2..x..0..x....2..x..0..x....2..x..1..x....0..x..1..x
..x..2..x..0....x..0..x..2....x..0..x..2....x..0..x..0....x..2..x..0
..1..x..1..x....2..x..1..x....2..x..1..x....2..x..2..x....1..x..2..x
CROSSREFS
Cf. A230708.
Sequence in context: A299415 A364078 A373904 * A365693 A168605 A127865
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 28 2013
STATUS
approved