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 A250642 #6 Jul 23 2025 12:38:32 %S A250642 1,65,89,1293,4853,34441,163043,915663,4537317,23671551,118358549, %T A250642 601565301,3011330309,15155615651,75845220727,380253505733, %U A250642 1902264449049,9522274036139,47624961772074,238244610944161,1191402062810086 %N A250642 Number of length n+1 0..4 arrays with the sum of the maximum of each adjacent pair multiplied by some arrangement of +-1 equal to zero. %C A250642 Column 4 of A250646 %H A250642 R. H. Hardin, <a href="/A250642/b250642.txt">Table of n, a(n) for n = 1..110</a> %e A250642 Some solutions for n=6 %e A250642 ..0....3....1....2....2....0....3....1....4....4....2....1....3....0....3....4 %e A250642 ..1....2....2....0....3....2....0....1....1....3....0....2....3....1....0....4 %e A250642 ..1....4....2....0....3....2....2....3....0....1....3....2....1....1....2....2 %e A250642 ..4....2....1....1....0....1....4....0....0....2....2....3....3....0....0....4 %e A250642 ..0....3....2....3....1....4....3....1....2....4....1....4....1....1....2....4 %e A250642 ..3....3....4....0....1....1....2....2....3....1....3....3....4....3....1....2 %e A250642 ..1....2....0....1....3....2....1....1....4....0....0....3....2....1....0....4 %K A250642 nonn %O A250642 1,2 %A A250642 _R. H. Hardin_, Nov 26 2014