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%I #7 Jul 24 2018 09:39:05
%S 1,3,7,15,31,61,121,241,481,961,1921,3839,7671,15327,30623,61185,
%T 122249,244257,488033,975105,1948289,3892739,7777807,15540287,
%U 31049951,62038717,123955185,247666113,494844193,988713281,1975478273,3947063807
%N Hilltop maps: number of n X 1 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or vertical neighbor in a random 0..4 n X 1 array.
%C Column 1 of A218288.
%H R. H. Hardin, <a href="/A218281/b218281.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = a(n-1) + a(n-2) + a(n-3) + a(n-4) + a(n-5) + a(n-6) + a(n-7) + a(n-8) + a(n-9).
%F Empirical g.f.: x*(1 + x + x^2 + x^3 + x^4)^2 / (1 - x - x^2 - x^3 - x^4 - x^5 - x^6 - x^7 - x^8 - x^9). - _Colin Barker_, Jul 24 2018
%e All solutions for n=3:
%e ..1....0....0....1....0....1....1
%e ..1....0....1....0....1....0....1
%e ..1....1....1....1....0....0....0
%Y Cf. A218288.
%K nonn
%O 1,2
%A _R. H. Hardin_, Oct 25 2012
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