cp's OEIS Frontend

A221440 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 n X 2 array.

%I A221440 #8 Aug 05 2018 08:20:36
%S A221440 3,9,31,105,355,1201,4063,13745,46499,157305,532159,1800281,6090307,
%T A221440 20603361,69700671,235795681,797691075,2698569577,9129195487,
%U A221440 30883847113,104479306403,353450961809,1195716038943,4045078385041,13684402155875
%N A221440 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 n X 2 array.
%C A221440 Column 2 of A221446.
%H A221440 R. H. Hardin, <a href="/A221440/b221440.txt">Table of n, a(n) for n = 1..210</a>
%F A221440 Empirical: a(n) = 3*a(n-1) + a(n-2) + a(n-3).
%F A221440 Empirical g.f.: x*(3 + x^2) / (1 - 3*x - x^2 - x^3). - _Colin Barker_, Aug 05 2018
%e A221440 Some solutions for n=3:
%e A221440 ..0..1....1..0....0..1....1..1....1..0....1..1....1..1....1..0....1..1....0..1
%e A221440 ..1..1....0..1....1..1....1..1....1..1....0..1....1..0....1..0....1..1....0..1
%e A221440 ..0..1....1..1....1..0....1..0....0..1....0..1....1..0....1..1....0..1....1..1
%Y A221440 Cf. A221446.
%K A221440 nonn
%O A221440 1,1
%A A221440 _R. H. Hardin_, Jan 17 2013