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A209521 Number of nX2 0..7 arrays with every 2X2 subblock containing exactly one value repeat, and new values 0..7 introduced in row major order.

%I A209521 #7 Jul 22 2025 21:47:36
%S A209521 2,6,57,700,10677,193676,4054358,95534880,2472405340,68613576496,
%T A209521 1999809519672,60231323048000,1853103730499696,57790053276242496,
%U A209521 1817609007303894496,57472115932658904064,1823283879810883824576
%N A209521 Number of nX2 0..7 arrays with every 2X2 subblock containing exactly one value repeat, and new values 0..7 introduced in row major order.
%C A209521 Column 2 of A209527
%H A209521 R. H. Hardin, <a href="/A209521/b209521.txt">Table of n, a(n) for n = 1..210</a>
%F A209521 Empirical: a(n) = 68*a(n-1) -1410*a(n-2) +5696*a(n-3) +105944*a(n-4) -757536*a(n-5) -1207008*a(n-6) +7568640*a(n-7) +13260672*a(n-8) +4354560*a(n-9) for n>10
%e A209521 Some solutions for n=5
%e A209521 ..0..0....0..0....0..0....0..0....0..0....0..0....0..1....0..0....0..0....0..0
%e A209521 ..1..2....1..2....1..2....1..2....1..2....1..2....0..2....1..2....1..2....1..2
%e A209521 ..0..1....0..1....0..2....0..0....0..0....1..3....0..1....0..0....0..0....1..3
%e A209521 ..2..0....0..2....3..0....3..4....1..2....0..3....3..3....1..2....2..3....0..0
%e A209521 ..0..1....1..0....0..1....0..3....2..0....3..4....2..0....0..0....0..0....1..2
%K A209521 nonn
%O A209521 1,1
%A A209521 _R. H. Hardin_ Mar 10 2012