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A270145 Number of n X 2 0..7 arrays with some element plus some horizontally, diagonally, antidiagonally or vertically adjacent neighbor totalling seven exactly once. 1
8, 1440, 85056, 4126368, 182257536, 7623445344, 307704553920, 12111206870304, 467855602824192, 17813625850002144, 670485480935347776, 25000461221001205920, 924950147066819934336, 33996076829066361534048 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 66*a(n-1) - 1021*a(n-2) - 2244*a(n-3) - 1156*a(n-4) for n>5.

Conjectures from Colin Barker, Jan 30 2019: (Start)

G.f.: 8*x*(1 - x)^2*(1 + 116*x + 4*x^2) / ((1 + x)^2*(1 - 34*x)^2).

a(n) = (48*(-383214*(-1)^n - 2660911*34^n + 35*(363562*(-1)^n + 115797*34^n)*n)) / 210644875 for n>1.

(End)

EXAMPLE

Some solutions for n=3:

..5..0. .3..3. .7..3. .2..2. .2..3. .5..7. .6..5. .5..3. .3..6. .6..3

..1..0. .0..7. .6..5. .4..3. .1..0. .4..3. .6..6. .4..1. .2..1. .4..0

..6..5. .1..1. .2..6. .7..6. .4..6. .7..5. .3..4. .5..5. .3..1. .0..2

CROSSREFS

Column 2 of A270150.

Sequence in context: A064073 A282889 A225068 * A201492 A172938 A252176

Adjacent sequences:  A270142 A270143 A270144 * A270146 A270147 A270148

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 12 2016

STATUS

approved

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Last modified September 19 04:52 EDT 2019. Contains 327187 sequences. (Running on oeis4.)