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 A225305 Number of nX4 -1,1 arrays such that the sum over i=1..n,j=1..4 of i*x(i,j) is zero and rows are nondecreasing (ways to put 4 thrusters pointing east or west at each of n positions 1..n distance from the hinge of a south-pointing gate without turning the gate) 1

%I #4 May 05 2013 06:28:36

%S 1,3,9,31,113,443,1787,7445,31593,136351,596187,2636015,11763569,

%T 52920569,239731317,1092632909,5006816043,23053197067,106601983853,

%U 494856940025,2305237337415,10772988573393,50491926308985

%N Number of nX4 -1,1 arrays such that the sum over i=1..n,j=1..4 of i*x(i,j) is zero and rows are nondecreasing (ways to put 4 thrusters pointing east or west at each of n positions 1..n distance from the hinge of a south-pointing gate without turning the gate)

%C Column 4 of A225310

%H R. H. Hardin, <a href="/A225305/b225305.txt">Table of n, a(n) for n = 1..210</a>

%e Some solutions for n=4

%e .-1..1..1..1...-1.-1.-1.-1...-1.-1..1..1...-1.-1.-1..1...-1.-1..1..1

%e .-1.-1.-1..1...-1.-1.-1.-1...-1.-1..1..1...-1.-1.-1..1...-1.-1.-1..1

%e .-1.-1.-1..1....1..1..1..1...-1.-1..1..1...-1..1..1..1...-1.-1.-1.-1

%e .-1..1..1..1...-1.-1..1..1...-1.-1..1..1...-1.-1..1..1....1..1..1..1

%K nonn

%O 1,2

%A _R. H. Hardin_ May 05 2013

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Last modified February 25 06:40 EST 2024. Contains 370310 sequences. (Running on oeis4.)