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A220561 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly one horizontal or antidiagonal neighbor.

%I A220561 #6 Jul 23 2025 01:13:28
%S A220561 21,1544,101052,6743873,449429440,29955561052,1996515036228,
%T A220561 133064181801048,8868465829053416,591065515195237024,
%U A220561 39393331961841054032,2625486595153945514656,174983417444316851450400
%N A220561 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly one horizontal or antidiagonal neighbor.
%C A220561 Column 7 of A220562
%H A220561 R. H. Hardin, <a href="/A220561/b220561.txt">Table of n, a(n) for n = 1..210</a>
%F A220561 Empirical: a(n) = 85*a(n-1) -1330*a(n-2) +7350*a(n-3) -15316*a(n-4) +12720*a(n-5) -3168*a(n-6) for n>9
%e A220561 Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10)
%e A220561 ..0..0..0..0..0..7..0....0..0..0..0..7..6..4....0..0..0..0..0..6..4
%e A220561 ..0..6..4..0..3..6..4....6..4..7..3..0..0..0....6..4..6..4..6..4..0
%e A220561 ..6..4..6..4..0..0..0....0..3..0..6..4..0..0....6..4..0..0..6..4..0
%K A220561 nonn
%O A220561 1,1
%A A220561 _R. H. Hardin_ Dec 16 2012