A235887 Number of (n+1) X (2+1) 0..3 arrays with the minimum plus the upper median equal to the lower median plus the maximum in every 2 X 2 subblock.

112, 232, 568, 1624, 5272, 18712, 70168, 271384, 1067032, 4231192, 16850968, 67256344, 268730392, 1074331672, 4296146968, 17182228504, 68724195352, 274887344152, 1099530502168, 4398084259864, 17592261541912, 70368895172632

Offset

1,1

Links

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

Formula

Empirical: a(n) = 7*a(n-1) - 14*a(n-2) + 8*a(n-3).

Conjectures from Colin Barker, Oct 19 2018: (Start)

G.f.: 8*x*(14 - 69*x + 64*x^2) / ((1 - x)*(1 - 2*x)*(1 - 4*x)).

a(n) = 4*(6 + 9*2^n + 4^n).

(End)

Example

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

Crossrefs

Column 2 of A235893.

Sequence in context: A349206 A217149 A119684 * A296579 A297970 A296185

Adjacent sequences: A235884 A235885 A235886 * A235888 A235889 A235890

Keyword

nonn

Author

R. H. Hardin, Jan 16 2014

Status

approved