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%I #4 Dec 18 2012 09:40:44
%S 1,21,230,2586,29310,331589,3751888,42452438,480346122,5435081884,
%T 61497557384,695840407309,7873383816355,89086767652576,
%U 1008010323915227,11405563810447637,129053128472692922,1460226802057078840
%N Number of ways to reciprocally link elements of an nX4 array either to themselves or to exactly two horizontal, diagonal or antidiagonal neighbors
%C Column 4 of A220725
%H R. H. Hardin, <a href="/A220721/b220721.txt">Table of n, a(n) for n = 1..210</a>
%F Empirical: a(n) = 9*a(n-1) +20*a(n-2) +64*a(n-3) +65*a(n-4) +51*a(n-5) -90*a(n-6) -76*a(n-7) -34*a(n-8) +21*a(n-9) +13*a(n-10) -a(n-11) -a(n-12)
%e Some solutions for n=3 0=self 1=nw 3=ne 4=w 6=e 7=sw 9=se (reciprocal directions total 10)
%e .69.47.00.00...00.79.69.47...00.79.79.00...00.00.00.00...00.00.69.47
%e .36.14.79.00...36.49.13.17...36.34.19.17...00.69.49.00...69.49.37.17
%e .00.36.46.14...00.00.13.00...00.00.36.14...00.00.16.14...00.13.13.00
%K nonn
%O 1,2
%A _R. H. Hardin_ Dec 18 2012
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