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%I #8 Jul 24 2018 16:31:53
%S 15,249,3969,63499,1015887,16252713,260019585,4159932363,66552822351,
%T 1064747639097,17034402072321,272525472991467,4360008241786383,
%U 69753743236473129,1115957683030959873,17853687738218017899
%N Hilltop maps: number of n X 4 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..3 n X 4 array.
%C Column 4 of A218810.
%H R. H. Hardin, <a href="/A218806/b218806.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 15*a(n-1) + 15*a(n-2) + 15*a(n-3) + 9*a(n-4) + 9*a(n-5) + 9*a(n-6) + 9*a(n-7).
%F Empirical g.f.: x*(15 + 24*x + 9*x^2 + 4*x^3 - 3*x^4 + 12*x^5 + 3*x^6) / (1 - 15*x - 15*x^2 - 15*x^3 - 9*x^4 - 9*x^5 - 9*x^6 - 9*x^7). - _Colin Barker_, Jul 24 2018
%e Some solutions for n=3:
%e ..0..0..1..0....1..0..1..0....1..0..1..0....1..0..0..0....1..0..1..0
%e ..1..1..1..0....1..0..1..0....0..0..0..1....1..0..1..1....0..1..1..0
%e ..1..0..0..0....1..0..0..0....0..1..1..1....0..1..1..0....1..1..1..0
%Y Cf. A218810.
%K nonn
%O 1,1
%A _R. H. Hardin_, Nov 06 2012
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