A220324 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..1 n X 3 array.
2, 16, 92, 508, 2788, 15316, 84196, 462940, 2545492, 13996468, 76959844, 423164812, 2326777444, 12793817140, 70346976484, 386803802332, 2126845944052, 11694491219668, 64302318307108, 353567167818892, 1944093859291588
Offset: 1
Keywords
Examples
Some solutions for n=3: ..0..1..1....0..1..1....0..1..1....0..0..1....0..0..0....0..0..1....0..0..0 ..1..0..1....0..1..0....0..0..0....0..1..1....1..1..0....1..0..1....0..0..1 ..0..0..0....1..1..0....0..0..0....0..0..0....1..1..0....0..0..0....0..1..0
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Crossrefs
Cf. A220328.
Formula
Empirical: a(n) = 7*a(n-1) - 9*a(n-2) + 3*a(n-3) + 6*a(n-4).
Empirical g.f.: 2*x*(1 + x - x^2 + x^3) / (1 - 7*x + 9*x^2 - 3*x^3 - 6*x^4). - Colin Barker, Jul 31 2018
Comments