cp's OEIS Frontend

A220613 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal and vertical neighbors, without consecutive collinear links.

%I A220613 #6 Jul 23 2025 01:17:39
%S A220613 1,21,85,781,4673,34981,233265,1653229,11354857,79290645,548972737,
%T A220613 3817993565,26491584361,184040357765,1277739038129,8873937621293,
%U A220613 61619077914745,427911161639829,2971470559369153,20634790487757629
%N A220613 Number of ways to reciprocally link elements of an nX7 array either to themselves or to exactly two horizontal and vertical neighbors, without consecutive collinear links.
%C A220613 Column 7 of A220614
%H A220613 R. H. Hardin, <a href="/A220613/b220613.txt">Table of n, a(n) for n = 1..210</a>
%F A220613 Empirical: a(n) = 5*a(n-1) +40*a(n-2) -144*a(n-3) -532*a(n-4) +1484*a(n-5) +3044*a(n-6) -6644*a(n-7) -8872*a(n-8) +13920*a(n-9) +13824*a(n-10) -13056*a(n-11) -10688*a(n-12) +4288*a(n-13) +3072*a(n-14)
%e A220613 Some solutions for n=3 0=self 2=n 4=w 6=e 8=s (reciprocal directions total 10)
%e A220613 .68.48.00.68.48.00.00...68.48.68.48.00.00.00...00.00.00.68.48.00.00
%e A220613 .26.24.00.26.24.00.00...26.24.26.24.00.68.48...00.00.00.26.24.68.48
%e A220613 .00.00.00.00.00.00.00...00.00.00.00.00.26.24...00.00.00.00.00.26.24
%K A220613 nonn
%O A220613 1,2
%A A220613 _R. H. Hardin_ Dec 17 2012