cp's OEIS Frontend

A220631 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal or antidiagonal neighbors.

%I A220631 #6 Jul 23 2025 01:19:19
%S A220631 1,32,564,10695,201903,3817452,72097810,1362188752,25734606523,
%T A220631 486186026515,9185167500820,173528846174065,3278357276282501,
%U A220631 61935676290875214,1170106754973419295,22105996097313109325
%N A220631 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal or antidiagonal neighbors.
%C A220631 Column 7 of A220632
%H A220631 R. H. Hardin, <a href="/A220631/b220631.txt">Table of n, a(n) for n = 1..210</a>
%F A220631 Empirical: a(n) = 11*a(n-1) +119*a(n-2) +510*a(n-3) +1074*a(n-4) +735*a(n-5) -1120*a(n-6) -2716*a(n-7) +5687*a(n-8) -4250*a(n-9) +1973*a(n-10) -802*a(n-11) +244*a(n-12) -36*a(n-13) -4*a(n-14)
%e A220631 Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10)
%e A220631 .00.00.00.00.00.67.47...00.67.47.67.47.67.47...00.67.46.47.00.67.47
%e A220631 .00.00.00.00.37.36.47...36.34.37.37.36.34.00...36.46.34.00.37.37.00
%e A220631 .00.00.00.36.46.34.00...00.36.34.00.00.00.00...00.00.00.36.34.00.00
%K A220631 nonn
%O A220631 1,2
%A A220631 _R. H. Hardin_ Dec 17 2012