A221425 - OEIS

A221425

Number of n X 2 arrays of occupancy after each element moves to some horizontal or vertical neighbor, without consecutive moves in the same direction.

1, 9, 42, 217, 1116, 5722, 29383, 150821, 774219, 3974308, 20401353, 104726538, 537593996, 2759637891, 14166083083, 72718928341, 373288968420, 1916208848267, 9836498426064, 50493818235236, 259200537583569, 1330557304472777

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OFFSET

1,2

COMMENTS

Column 2 of A221429.

LINKS

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

FORMULA

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

Empirical g.f.: x*(1 + 5*x - 5*x^3 + x^4) / (1 - 4*x - 6*x^2 + 5*x^4 - x^5). - Colin Barker, Aug 05 2018

EXAMPLE

Some solutions for n=3: