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%I #12 May 04 2018 22:41:07
%S 1,9,25,105,369,1393,5105,18937,69897,258521,955361,3531745,13054177,
%T 48254185,178365177,659309641,2437064529,9008352081,33298400977,
%U 123083978969,454966715881,1681735706553,6216355687361,22978092329921
%N Number of arrays of -4..4 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero.
%C Column 4 of A193648.
%H R. H. Hardin, <a href="/A193644/b193644.txt">Table of n, a(n) for n = 1..200</a>
%F Empirical: a(n) = 2*a(n-1) +6*a(n-2) +a(n-3).
%F Empirical g.f.: x*(1 + 7*x + x^2) / (1 - 2*x - 6*x^2 - x^3). - _Colin Barker_, May 04 2018
%e Some solutions for n=6:
%e -2 2 -3 -4 3 3 3 0 0 0 -2 -4 4 4 0 2
%e 2 -2 3 4 -3 -3 -3 1 -3 4 2 4 -4 -4 -4 -2
%e -2 0 0 -1 3 3 3 -1 3 -4 -2 4 4 2 4 2
%e -2 -3 3 1 -3 0 3 0 2 -2 -2 -4 0 -2 3 0
%e 2 3 -3 -1 3 4 -3 -4 -2 2 2 -3 -4 -2 -3 -3
%e -2 0 3 1 0 -4 0 4 2 -2 0 3 4 2 0 3
%Y Cf. A193648.
%K nonn
%O 1,2
%A _R. H. Hardin_, Aug 02 2011