cp's OEIS Frontend

A218657 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 2 array.

%I A218657 #8 Mar 10 2018 07:15:01
%S A218657 3,15,57,225,891,3519,13905,54945,217107,857871,3389769,13394241,
%T A218657 52925643,209128959,826346529,3265203393,12902036643,50980759695,
%U A218657 201443999193,795980386593,3145215436443,12427919466687,49107345869169
%N A218657 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any king-move neighbor in a random 0..1 n X 2 array.
%C A218657 Column 2 of A218663.
%H A218657 R. H. Hardin, <a href="/A218657/b218657.txt">Table of n, a(n) for n = 1..210</a>
%F A218657 Empirical: a(n) = 3*a(n-1) + 3*a(n-2) + 3*a(n-3).
%F A218657 Empirical g.f.: 3*x*(1 + x)^2 / (1 - 3*x - 3*x^2 - 3*x^3). - _Colin Barker_, Mar 10 2018
%e A218657 Some solutions for n=3:
%e A218657 ..1..1....1..1....1..0....0..0....1..1....0..1....0..1....0..0....1..1....0..0
%e A218657 ..1..1....1..0....1..1....0..1....0..1....0..0....1..0....1..0....0..1....0..1
%e A218657 ..1..1....0..1....1..1....0..0....0..1....1..0....0..1....1..1....0..0....0..1
%Y A218657 Cf. A218663.
%K A218657 nonn
%O A218657 1,1
%A A218657 _R. H. Hardin_, Nov 04 2012