cp's OEIS Frontend

A220557 Number of ways to reciprocally link elements of an n X n array either to themselves or to exactly one horizontal or antidiagonal neighbor.

%I A220557 #8 Jul 23 2025 01:13:15
%S A220557 1,5,64,3966,810778,665748170,1996515036228,22849956206052338,
%T A220557 978504298175393645420,158156973836014224403041023,
%U A220557 96121270674841350006417715266220
%N A220557 Number of ways to reciprocally link elements of an n X n array either to themselves or to exactly one horizontal or antidiagonal neighbor.
%C A220557 Diagonal of A220562
%H A220557 R. H. Hardin, <a href="/A220557/b220557.txt">Table of n, a(n) for n = 1..18</a>
%e A220557 Some solutions for n=3 0=self 3=ne 4=w 6=e 7=sw (reciprocal directions total 10)
%e A220557 ..0..6..4....0..7..7....0..6..4....6..4..7....6..4..0....0..7..7....0..7..7
%e A220557 ..0..6..4....3..3..7....0..7..0....0..3..0....0..7..7....3..3..0....3..3..0
%e A220557 ..0..6..4....0..3..0....3..0..0....0..0..0....3..3..0....0..0..0....6..4..0
%K A220557 nonn
%O A220557 1,2
%A A220557 _R. H. Hardin_ Dec 16 2012