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%I A210900 #6 Dec 18 2015 18:18:05
%S A210900 1,5,102,6390,1086041,502575673,633196217205,2172041686544831,
%T A210900 20286478141700961127,515885869356108286483984,
%U A210900 35719903989356689494965133243,6734055759629373955660905711394302
%N A210900 Number of n X n 0..2 symmetric matrices with every element equal to zero, one or two horizontal and vertical neighbors, and new values 0..2 introduced in lower triangle row major order
%H A210900 R. H. Hardin, <a href="/A210900/b210900.txt">Table of n, a(n) for n = 1..13</a>
%e A210900 Some solutions for n=4
%e A210900 ..0..1..0..1....0..1..2..2....0..0..1..1....0..1..1..2....0..0..1..1
%e A210900 ..1..0..1..1....1..1..0..1....0..1..2..0....1..1..0..0....0..1..0..0
%e A210900 ..0..1..1..2....2..0..2..0....1..2..1..2....1..0..1..0....1..0..2..2
%e A210900 ..1..1..2..2....2..1..0..1....1..0..2..2....2..0..0..1....1..0..2..0
%K A210900 nonn
%O A210900 1,2
%A A210900 _R. H. Hardin_ Mar 29 2012

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