A270112 Number of n X 2 0..7 arrays with some element plus some horizontally or vertically adjacent neighbor totalling seven exactly once.

8, 1344, 100800, 6183744, 345422784, 18272616768, 932758314432, 46431146637120, 2268408487407552, 109231939785014592, 5199659528294691264, 245200862770851468096, 11473103730476342109120, 533310525557661056874816

Offset

1,1

Links

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

Formula

Empirical: a(n) = 86*a(n-1) - 1849*a(n-2) for n>3.

Conjectures from Colin Barker, Jan 29 2019: (Start)

G.f.: 8*x*(1 + 82*x + x^2) / (1 - 43*x)^2.

a(n) = 1344*43^(n-3) * (32*n-21) for n>1.

(End)

Example

Some solutions for n=3:
..0..1. .1..5. .4..5. .5..6. .2..5. .7..0. .2..0. .7..7. .4..0. .3..1
..0..3. .5..4. .3..7. .1..4. .2..4. .4..6. .2..3. .2..0. .6..7. .4..5
..7..5. .1..3. .0..3. .1..3. .1..2. .5..5. .5..0. .6..2. .6..5. .7..5

Crossrefs

Column 2 of A270118.

Sequence in context: A017187 A168575 A286315 * A281127 A001418 A123268

Adjacent sequences: A270109 A270110 A270111 * A270113 A270114 A270115

Keyword

nonn

Author

R. H. Hardin, Mar 11 2016

Status

approved