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A216985 Number of city-block distance 1, pressure limit 2 movements in an n X 2 array with each element moving exactly one horizontally or vertically, no element acquiring more than two neighbors, and without 2-loops. 1
0, 2, 14, 80, 436, 2346, 12578, 67368, 360720, 1931306, 10340030, 55359176, 296385268, 1586804322, 8495522018, 45483800496, 243513709632, 1303737284978, 6980021408654, 37370028005408, 200073740644948, 1071165953874618 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Column 2 of A216991.

LINKS

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

FORMULA

Empirical: a(n) = 7*a(n-1) - 9*a(n-2) + a(n-3).

Empirical g.f.: 2*x^2 / (1 - 7*x + 9*x^2 - x^3). - Colin Barker, Jul 23 2018

EXAMPLE

Some solutions for n=3 (movement: 0=n 1=e 2=s 3=w):

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

..1..2....2..3....1..2....1..0....1..0....0..3....0..2....0..3....1..2....2..0

..0..3....1..0....0..3....1..0....0..3....0..0....0..3....1..0....0..3....1..0

CROSSREFS

Cf. A216991.

Sequence in context: A112408 A026291 A220867 * A102401 A077461 A077444

Adjacent sequences:  A216982 A216983 A216984 * A216986 A216987 A216988

KEYWORD

nonn

AUTHOR

R. H. Hardin, Sep 21 2012

STATUS

approved

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Last modified March 23 14:17 EDT 2019. Contains 321431 sequences. (Running on oeis4.)