

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 southpointing gate without turning the gate)


1



1, 3, 9, 31, 113, 443, 1787, 7445, 31593, 136351, 596187, 2636015, 11763569, 52920569, 239731317, 1092632909, 5006816043, 23053197067, 106601983853, 494856940025, 2305237337415, 10772988573393, 50491926308985
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OFFSET

1,2


COMMENTS



LINKS



EXAMPLE

Some solutions for n=4
.1..1..1..1...1.1.1.1...1.1..1..1...1.1.1..1...1.1..1..1
.1.1.1..1...1.1.1.1...1.1..1..1...1.1.1..1...1.1.1..1
.1.1.1..1....1..1..1..1...1.1..1..1...1..1..1..1...1.1.1.1
.1..1..1..1...1.1..1..1...1.1..1..1...1.1..1..1....1..1..1..1


CROSSREFS



KEYWORD

nonn


AUTHOR



STATUS

approved



