cp's OEIS Frontend

A220549 Number of ways to reciprocally link elements of an nX4 array either to themselves or to exactly one horizontal, vertical or antidiagonal neighbor.

%I A220549 #6 Jul 23 2025 01:12:41
%S A220549 5,108,1814,32173,565061,9943416,174911750,3077034244,54130248568,
%T A220549 952245176313,16751640356635,294690365449276,5184113807856060,
%U A220549 91197538858856819,1604322628219475789,28222813114190945744
%N A220549 Number of ways to reciprocally link elements of an nX4 array either to themselves or to exactly one horizontal, vertical or antidiagonal neighbor.
%C A220549 Column 4 of A220553
%H A220549 R. H. Hardin, <a href="/A220549/b220549.txt">Table of n, a(n) for n = 1..210</a>
%F A220549 Empirical: a(n) = 11*a(n-1) +111*a(n-2) +127*a(n-3) -649*a(n-4) -981*a(n-5) +1615*a(n-6) +2067*a(n-7) -2349*a(n-8) -1177*a(n-9) +1383*a(n-10) +199*a(n-11) -337*a(n-12) +3*a(n-13) +31*a(n-14) -a(n-15) -a(n-16)
%e A220549 Some solutions for n=3 0=self 2=n 3=ne 4=w 6=e 7=sw 8=s (reciprocal directions total 10)
%e A220549 ..6..4..7..8....0..0..6..4....6..4..7..7....8..8..0..7....6..4..7..7
%e A220549 ..0..3..0..2....0..7..0..8....0..3..3..0....2..2..3..0....0..3..3..0
%e A220549 ..6..4..6..4....3..0..0..2....6..4..0..0....0..0..0..0....6..4..6..4
%K A220549 nonn
%O A220549 1,1
%A A220549 _R. H. Hardin_ Dec 15 2012