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A201081 Number of -1..1 arrays of n elements with first and second differences also in -1..1.

%I A201081 #9 Feb 15 2018 08:12:10
%S A201081 3,7,13,25,47,89,169,321,609,1155,2191,4157,7887,14963,28387,53855,
%T A201081 102173,193841,367751,697689,1323641,2511185,4764169,9038483,17147623,
%U A201081 32532117,61719263,117092515,222145507,421449879,799566029,1516920201
%N A201081 Number of -1..1 arrays of n elements with first and second differences also in -1..1.
%C A201081 Column 1 of A201088.
%H A201081 R. H. Hardin, <a href="/A201081/b201081.txt">Table of n, a(n) for n = 1..210</a>
%F A201081 Empirical: a(n) = 2*a(n-1) -a(n-2) +a(n-3) +a(n-4).
%F A201081 Empirical g.f.: x*(3 + 2*x + x^2)*(1 + 3*x^2 - 2*x^3 + x^4) / ((1 - x)^3*(1 + x + x^2)^2). - _Colin Barker_, Feb 15 2018
%e A201081 Some solutions for n=10:
%e A201081 ..1....1....1...-1....1....0....0...-1....1....1....1....1....0....0....0...-1
%e A201081 ..1....0....0...-1....0....0...-1...-1....0....0....1....0...-1....1....1...-1
%e A201081 ..0...-1....0....0....0...-1...-1....0...-1...-1....1...-1...-1....1....1....0
%e A201081 .-1...-1....0....0....1...-1....0....1...-1...-1....0...-1....0....1....1....0
%e A201081 .-1...-1....0....1....1....0....0....1....0...-1....0....0....1....0....1....0
%e A201081 .-1...-1...-1....1....0....0...-1....0....0...-1...-1....0....1...-1....1...-1
%e A201081 ..0...-1...-1....1....0....0...-1...-1....0...-1...-1....0....0...-1....1...-1
%e A201081 ..0....0...-1....0....0....1...-1...-1....0...-1....0....0....0...-1....1...-1
%e A201081 ..0....0....0....0....1....1....0...-1...-1....0....0....0....0...-1....0....0
%e A201081 ..1....0....1...-1....1....1....1...-1...-1....1...-1....1...-1...-1....0....0
%K A201081 nonn
%O A201081 1,1
%A A201081 _R. H. Hardin_, Nov 26 2011