cp's OEIS Frontend

A225309 Number of nX8 -1,1 arrays such that the sum over i=1..n,j=1..8 of i*x(i,j) is zero and rows are nondecreasing (ways to put 8 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 A225309 #6 Jun 02 2025 08:32:09
%S A225309 1,5,27,175,1165,8221,60007,449693,3437315,26700429,210147859,
%T A225309 1672294243,13432357463,108761156653,886785526897,7274670122017,
%U A225309 59999774031797,497244626964801,4138638973241695,34580160863858515,289947745327853737
%N A225309 Number of nX8 -1,1 arrays such that the sum over i=1..n,j=1..8 of i*x(i,j) is zero and rows are nondecreasing (ways to put 8 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 A225309 Column 8 of A225310
%H A225309 R. H. Hardin, <a href="/A225309/b225309.txt">Table of n, a(n) for n = 1..210</a>
%e A225309 Some solutions for n=4
%e A225309 .-1.-1..1..1..1..1..1..1...-1..1..1..1..1..1..1..1...-1.-1.-1.-1.-1..1..1..1
%e A225309 .-1.-1.-1.-1.-1..1..1..1...-1.-1.-1.-1.-1.-1..1..1....1..1..1..1..1..1..1..1
%e A225309 .-1.-1.-1.-1..1..1..1..1...-1.-1.-1.-1.-1..1..1..1...-1.-1.-1.-1.-1..1..1..1
%e A225309 .-1.-1.-1.-1..1..1..1..1...-1.-1.-1..1..1..1..1..1...-1.-1.-1.-1.-1..1..1..1
%K A225309 nonn
%O A225309 1,2
%A A225309 _R. H. Hardin_ May 05 2013