This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A188350 #7 Jul 22 2025 11:09:14 %S A188350 5,15,29,91,197,627,1477,4671,11693,36487,95405,293695,792525,2412175, %T A188350 6660989,20097243,56450693,169229571,481426405,1436666475,4126292293, %U A188350 12275100443,35511918037,105423983379,306684489749,909271908483 %N A188350 Number of arrangements of n+1 numbers x(i) in -1..1 with the sum of x(i)*x(i+1) equal to zero. %C A188350 Column 1 of A188358 %H A188350 R. H. Hardin, <a href="/A188350/b188350.txt">Table of n, a(n) for n = 1..200</a> %e A188350 Some solutions for n=4 %e A188350 ..1....0....1...-1....0...-1....1....0....1...-1....0....0...-1...-1...-1....0 %e A188350 ..0....0....0....0....0...-1....0....1....1....0....0....0....1....0....0....0 %e A188350 .-1...-1....1....1...-1....1...-1...-1....0...-1...-1...-1....1....0....0....1 %e A188350 .-1....0....0...-1....0....0....0...-1...-1....1....0...-1....0....0...-1....1 %e A188350 ..1....1...-1...-1...-1....1...-1....0....1....1....0....1...-1...-1....0...-1 %K A188350 nonn %O A188350 1,1 %A A188350 _R. H. Hardin_ Mar 28 2011