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A270052
Number of nX2 0..4 arrays with some element plus some horizontally or vertically adjacent neighbor totalling four exactly once.
1
5, 240, 5400, 99840, 1683240, 26891280, 414705720, 6237722400, 92095515720, 1340308323120, 19283874244440, 274868623748160, 3887609470141800, 54625048810247760, 763245268612477560, 10612743734992545120
OFFSET
1,1
COMMENTS
Column 2 of A270058.
LINKS
FORMULA
Empirical: a(n) = 26*a(n-1) -169*a(n-2) for n>3.
Empirical: g.f. 5*x -120*x^2*(-2+7*x) / (13*x-1)^2 . - R. J. Mathar, Mar 09 2016
EXAMPLE
Some solutions for n=4
..3..3. .1..0. .2..3. .1..4. .2..0. .3..3. .4..4. .1..2. .4..4. .4..1
..3..2. .1..3. .0..0. .2..3. .3..0. .2..2. .1..4. .2..0. .1..3. .2..0
..0..3. .4..4. .3..1. .0..0. .4..0. .4..4. .4..2. .1..2. .1..2. .1..2
..1..3. .2..4. .3..0. .2..4. .4..2. .3..2. .3..1. .1..2. .4..4. .3..3
CROSSREFS
Cf. A270058.
Sequence in context: A140518 A269551 A200962 * A174767 A230885 A142732
KEYWORD
nonn
AUTHOR
R. H. Hardin, Mar 09 2016
STATUS
approved