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A209368 Number of n X 2 1..3 arrays with no element with value z exactly a city block distance of z from another element with value z. 1
8, 39, 84, 129, 178, 338, 722, 1568, 3362, 7200, 15488, 33282, 71442, 153458, 329672, 708050, 1520768, 3266568, 7016258, 15070050, 32369058, 69525632, 149333762, 320753792, 688947200, 1479788802, 3178436450, 6826961250, 14663623752 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Column 2 of A209374.

LINKS

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

FORMULA

Empirical: a(n) = a(n-1) + a(n-2) + 3*a(n-3) + a(n-4) - a(n-5) - a(n-6) for n>11.

Empirical g.f.: x*(8 + 31*x + 37*x^2 - 18*x^3 - 160*x^4 - 252*x^5 - 218*x^6 - 32*x^7 + 93*x^8 + 73*x^9 + 16*x^10) / ((1 + x^2 - x^3)*(1 - x - 2*x^2 - x^3)). - Colin Barker, Jul 09 2018

EXAMPLE

Some solutions for n=5:

..3..2....3..1....3..1....3..2....2..3....2..1....2..2....2..1....2..3....3..1

..1..2....2..3....1..2....1..3....2..1....1..3....1..3....2..3....2..1....1..3

..3..1....2..1....3..1....3..1....1..3....3..3....3..1....3..3....1..3....2..1

..1..3....1..3....1..3....2..3....3..2....1..3....1..3....1..3....3..1....1..3

..2..1....3..1....2..1....2..1....1..2....2..2....2..1....2..1....1..2....3..2

CROSSREFS

Cf. A209374.

Sequence in context: A196074 A329172 A003353 * A190097 A245135 A200157

Adjacent sequences:  A209365 A209366 A209367 * A209369 A209370 A209371

KEYWORD

nonn

AUTHOR

R. H. Hardin, Mar 07 2012

STATUS

approved

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Last modified September 22 21:07 EDT 2020. Contains 337291 sequences. (Running on oeis4.)