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%I #7 Mar 09 2015 04:32:06
%S 1,3,121,771,317259,4380445,18838482047,567241901289,
%T 25690815631493191,1691995329032459285,809857047207692689731131,
%U 116848319343974137914103093,592161880926391194661929563951461
%N Number of n X n integer matrices, symmetric under horizontal reflection, with adjacent elements differing by no more than 1, counting matrices differing by a constant only once.
%H R. H. Hardin, Aug 06 2008, <a href="/A141440/b141440.txt">Table of n, a(n) for n = 1..18</a>
%K nonn
%O 1,2
%A _R. H. Hardin_, Aug 06 2008