A221420 - OEIS

A221420

Number of 2 X n arrays of occupancy after each element stays put or moves to some horizontal or antidiagonal neighbor, with every occupancy equal to zero or two.

0, 4, 10, 29, 84, 242, 696, 2000, 5744, 16492, 47344, 135900, 390080, 1119636, 3213616, 9223756, 26474016, 75985524, 218092816, 625967180, 1796642240, 5156696372, 14800673136, 42480669068, 121927372384, 349954089588

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OFFSET

1,2

COMMENTS

Row 2 of A221419.

LINKS

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

FORMULA

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

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

EXAMPLE

Some solutions for n=3: