cp's OEIS Frontend

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).

%I A225305 #6 Jun 02 2025 08:31:48
%S A225305 1,3,9,31,113,443,1787,7445,31593,136351,596187,2636015,11763569,
%T A225305 52920569,239731317,1092632909,5006816043,23053197067,106601983853,
%U A225305 494856940025,2305237337415,10772988573393,50491926308985
%N 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).
%C A225305 Column 4 of A225310
%H A225305 R. H. Hardin, <a href="/A225305/b225305.txt">Table of n, a(n) for n = 1..210</a>
%e A225305 Some solutions for n=4
%e A225305 .-1..1..1..1...-1.-1.-1.-1...-1.-1..1..1...-1.-1.-1..1...-1.-1..1..1
%e A225305 .-1.-1.-1..1...-1.-1.-1.-1...-1.-1..1..1...-1.-1.-1..1...-1.-1.-1..1
%e A225305 .-1.-1.-1..1....1..1..1..1...-1.-1..1..1...-1..1..1..1...-1.-1.-1.-1
%e A225305 .-1..1..1..1...-1.-1..1..1...-1.-1..1..1...-1.-1..1..1....1..1..1..1
%K A225305 nonn
%O A225305 1,2
%A A225305 _R. H. Hardin_ May 05 2013