A220932 Equals two maps: number of n X 3 binary arrays indicating the locations of corresponding elements equal to exactly two of their horizontal and antidiagonal neighbors in a random 0..2 n X 3 array.

2, 16, 92, 556, 3332, 19996, 119972, 719836, 4319012, 25914076, 155484452, 932906716, 5597440292, 33584641756, 201507850532, 1209047103196, 7254282619172, 43525695715036, 261154174290212, 1566925045741276

Offset

1,1

Comments

Column 3 of A220935.

Links

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

Formula

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

Conjectures from Colin Barker, Mar 13 2018: (Start)

G.f.: 2*x*(1 + 3*x) / ((1 + x)*(1 - 6*x)).

a(n) = (2^n*3^(n+1) + 4) / 7 for n even.

a(n) = (2^n*3^(n+1) - 4) / 7 for n odd

(End)

Example

Some solutions for n=3:
..0..1..0....0..1..1....0..1..0....0..0..0....0..0..0....0..1..0....0..0..0
..0..0..1....1..0..1....0..1..0....1..0..1....0..0..1....0..0..0....0..1..0
..1..1..0....1..0..0....0..1..0....1..0..0....0..1..0....1..1..0....1..0..0

Crossrefs

Cf. A220935.

Sequence in context: A317451 A220324 A208002 * A207558 A207413 A271273

Adjacent sequences: A220929 A220930 A220931 * A220933 A220934 A220935

Keyword

nonn

Author

R. H. Hardin, Dec 25 2012

Status

approved