A268635 - OEIS

A268635

Number of n_X_4 0..2 arrays with some element plus some horizontally or vertically adjacent neighbor totalling two exactly once.

36, 504, 5178, 47640, 412740, 3440052, 27906474, 221913216, 1737860310, 13445785116, 103012659468, 782824552488, 5908380409134, 44334271544616, 330997648937706, 2460394469263680, 18218335277707956, 134439600276305244

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OFFSET

1,1

LINKS

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

FORMULA

Empirical: a(n) = 18*a(n-1) - 111*a(n-2) + 282*a(n-3) - 333*a(n-4) + 180*a(n-5) - 36*a(n-6) for n>7.

Empirical g.f.: 6*x*(6 - 24*x + 17*x^2 + 38*x^3 - 27*x^4 - 12*x^5 + 8*x^6) / (1 - 9*x + 15*x^2 - 6*x^3)^2. - Colin Barker, Jan 14 2019

EXAMPLE

Some solutions for n=4:

..0..0..1..0. .0..0..1..0. .2..1..2..1. .1..2..2..2. .2..1..0..1

..0..0..0..1. .2..1..0..1. .2..2..1..0. .0..2..2..1. .2..2..1..0

..1..0..1..0. .2..2..1..0. .1..1..0..0. .1..2..1..0. .1..2..1..0

..1..0..0..1. .2..1..2..1. .0..0..1..0. .2..1..2..1. .2..1..0..0

CROSSREFS

Column 4 of A268639.

Sequence in context: A128986 A281371 A090408 * A233101 A183616 A008657

Adjacent sequences: A268632 A268633 A268634 * A268636 A268637 A268638

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 09 2016

STATUS

approved