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 A265229 #12 Feb 27 2025 07:57:13 %S A265229 1,2,7,43,372,4027,51871,773186,13083385,247698481,5186925696, %T A265229 119023766737,2969884019977,80056947698498,2318432654628847, %U A265229 71785166633148187,2366425763631216756,82748313392542136011 %N A265229 Number of n X 2 arrays containing 2 copies of 0..n-1 with no equal vertical neighbors and new values introduced sequentially from 0. %H A265229 Dmitry Efimov, <a href="https://arxiv.org/abs/2101.09722">Hafnian of two-parameter matrices</a>, arXiv:2101.09722 [math.CO], 2021. %e A265229 Some solutions for n=4: %e A265229 ..0..1....0..1....0..0....0..0....0..1....0..1....0..1....0..1....0..1....0..1 %e A265229 ..2..0....2..3....1..2....1..1....2..3....2..3....2..0....2..2....2..3....2..3 %e A265229 ..3..2....1..2....3..1....2..2....3..1....3..0....1..3....0..1....3..0....1..0 %e A265229 ..1..3....3..0....2..3....3..3....0..2....1..2....3..2....3..3....2..1....3..2 %Y A265229 Column 2 of A265232. %K A265229 nonn,more %O A265229 1,2 %A A265229 _R. H. Hardin_, Dec 06 2015