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%I #6 Dec 18 2015 18:18:13
%S 0,2,264,280900,2891592224,307860650044792,342045101062468307160,
%T 3979259269110908593906417328,485168384985330726560602698774047840,
%U 620116995791586597194849424436942942331423388
%N Number of city-block distance 1, pressure limit 2 movements in an n X n array with each element moving exactly one horizontally or vertically, no element acquiring more than two neighbors, and without 2-loops
%C Diagonal of A216991
%H R. H. Hardin, <a href="/A216984/b216984.txt">Table of n, a(n) for n = 1..11</a>
%e Some solutions for n=3 (movement: 0=n 1=e 2=s 3=w)
%e ..1..2..3....1..2..3....2..3..3....1..2..3....1..2..3....1..1..2....2..3..3
%e ..2..2..3....0..3..2....1..2..0....1..1..0....0..3..3....0..2..3....2..0..3
%e ..1..1..0....0..3..3....0..3..3....0..3..3....0..1..0....0..1..0....1..0..0
%K nonn
%O 1,2
%A _R. H. Hardin_ Sep 21 2012
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