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A270112
Number of n X 2 0..7 arrays with some element plus some horizontally or vertically adjacent neighbor totalling seven exactly once.
1
8, 1344, 100800, 6183744, 345422784, 18272616768, 932758314432, 46431146637120, 2268408487407552, 109231939785014592, 5199659528294691264, 245200862770851468096, 11473103730476342109120, 533310525557661056874816
OFFSET
1,1
LINKS
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 11 2016
STATUS
approved