A216987 - OEIS

A216987

Number of city-block distance 1, pressure limit 2 movements in an nX4 array with each element moving exactly one horizontally or vertically, no element acquiring more than two neighbors, and without 2-loops

%I #4 Sep 21 2012 17:01:23

%S 0,80,4794,280900,15836932,886416182,49491906456,2761454361344,

%T 154047246448662,8592994055896310,479322218408145970,

%U 26736736612809407136,1491380920762839897984,83189511828057155698994

%N Number of city-block distance 1, pressure limit 2 movements in an nX4 array with each element moving exactly one horizontally or vertically, no element acquiring more than two neighbors, and without 2-loops

%C Column 4 of A216991

%H R. H. Hardin, <a href="/A216987/b216987.txt">Table of n, a(n) for n = 1..210</a>

%F Empirical: a(n) = 84*a(n-1) -1756*a(n-2) +9538*a(n-3) +41862*a(n-4) -461584*a(n-5) +1025726*a(n-6) +76920*a(n-7) -2075057*a(n-8) +1315158*a(n-9) +48430*a(n-10) +125844*a(n-11) -68128*a(n-12) +6896*a(n-13) -7808*a(n-14) +780*a(n-15) -4*a(n-16)

%e Some solutions for n=3 (movement: 0=n 1=e 2=s 3=w)

%e ..1..1..2..3....1..1..2..3....2..3..1..2....2..3..3..3....2..3..3..2

%e ..1..0..1..0....0..3..3..0....1..0..2..3....2..3..0..2....1..0..3..3

%e ..0..3..1..0....1..1..1..0....0..3..1..0....1..1..0..3....0..1..0..0

%K nonn

%O 1,2

%A _R. H. Hardin_ Sep 21 2012