A218420 - OEIS

%I #7 Mar 10 2018 04:53:43

%S 3,13,49,191,737,2849,11011,42557,164481,635711,2456993,9496161,

%T 36702211,141852301,548252401,2118969471,8189716289,31652864193,

%U 122336815619,472825977597,1827449929601,7063007117695,27298186799297,105506194473793

%N Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal, vertical or antidiagonal neighbor in a random 0..1 n X 2 array.

%C Column 2 of A218426.

%H R. H. Hardin, <a href="/A218420/b218420.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + a(n-3) + a(n-4) + a(n-5).

%F Empirical g.f.: x*(3 + 4*x + x^2 + 2*x^3 + x^4) / (1 - 3*x - 3*x^2 - x^3 - x^4 - x^5). - _Colin Barker_, Mar 10 2018

%e Some solutions for n=3:

%e ..1..1....0..1....1..1....0..0....0..1....0..0....1..0....1..1....0..1....1..0

%e ..0..0....1..1....0..0....1..1....0..1....1..0....0..0....1..0....1..0....1..0

%e ..0..1....0..1....1..1....1..1....1..1....1..1....1..0....1..0....1..1....1..1

%Y Cf. A218426.

%K nonn

%O 1,1

%A _R. H. Hardin_, Oct 28 2012