A251143 Number of (n+1) X (2+1) 0..2 arrays with every 2 X 2 subblock summing to 4 and no 2 X 2 subblock having exactly two nonzero entries.

27, 49, 87, 161, 299, 565, 1075, 2065, 3991, 7761, 15163, 29749, 58563, 115617, 228791, 453633, 900875, 1791413, 3566099, 7105137, 14166487, 28262129, 56409627, 112633781, 224967459, 449449345, 898113015, 1794954785, 3587852651

Offset

1,1

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 3*a(n-1) - 5*a(n-3) + a(n-4) + 2*a(n-5).

Empirical g.f.: x*(27 - 32*x - 60*x^2 + 35*x^3 + 34*x^4) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 - x - x^2)). - Colin Barker, Nov 26 2018

Example

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

Crossrefs

Column 2 of A251149.

Sequence in context: A031325 A090761 A090760 * A109067 A034595 A330279

Adjacent sequences: A251140 A251141 A251142 * A251144 A251145 A251146

Keyword

nonn

Author

R. H. Hardin, Nov 30 2014

Status

approved