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 A309260 #48 Oct 24 2022 15:13:07 %S A309260 1,1,1,5,29,224,3012,55200,1259794,35488536,1200819600 %N A309260 Number of ways of placing 2n-1 nonattacking rooks on a hexagonal board with edge-length n in Glinski's hexagonal chess, inequivalent up to rotations and reflections of the board. %C A309260 A rook in Glinski's hexagonal chess can move to any cell along the perpendicular bisector of any of the 6 edges of the hexagonal cell it's on (analogous to a rook in orthodox chess which can move to any cell along the perpendicular bisector of any of the 4 edges of the square cell it's on). %H A309260 Alain Brobecker, <a href="http://abrobecker.free.fr/text/NonAttackingRooks.pdf">Non Attacking Rooks on Hexhex and Triangular boards</a> %H A309260 Chess variants, <a href="https://www.chessvariants.com/hexagonal.dir/hexagonal.html">Glinski's Hexagonal Chess</a> %H A309260 Vaclav Kotesovec, <a href="/A309260/a309260.jpg">All inequivalent solutions for n = 2,3,4 and 5</a> %H A309260 Wikipedia, <a href="https://en.wikipedia.org/wiki/Hexagonal_chess#Gli%C5%84ski's_hexagonal_chess">Hexagonal chess - Gliński's hexagonal chess</a> %e A309260 a(1) = 1 %e A309260 . %e A309260 o %e A309260 . %e A309260 a(2) = 1 %e A309260 . %e A309260 o . %e A309260 . . o %e A309260 o . %e A309260 . %e A309260 a(3) = 1 %e A309260 . %e A309260 o . . %e A309260 . . o . %e A309260 . . . . o %e A309260 o . . . %e A309260 . o . %e A309260 . %e A309260 a(4) = 5 %e A309260 . %e A309260 o . . . o . . . o . . . . o . . . o . . %e A309260 . . o . . . . o . . . . . o . o . . . . . . . . o %e A309260 . . . . o . . . . . . o . . . . . o . . . . . o o . . . . . %e A309260 . . . . . . o . o . . . . . . . o . . . . . . . o . . . . . . o . . . %e A309260 o . . . . . . . . . . o o . . . . . . . . . . o . . . . . o %e A309260 . o . . . . . o . . . . . . o o . . . . o . . . . %e A309260 . . o . o . . . . o . . . o . . . . o . %e A309260 . %Y A309260 Cf. A000903, A002047, A003215, A309746, A309669. %K A309260 nonn,more,hard %O A309260 1,4 %A A309260 _Sangeet Paul_, Jul 19 2019 %E A309260 a(1)-a(7) confirmed by _Vaclav Kotesovec_, Aug 16 2019 %E A309260 a(8) from _Alain Brobecker_, Dec 10 2021 %E A309260 a(8) confirmed by _Vaclav Kotesovec_, Dec 12 2021 %E A309260 a(9) from _Alain Brobecker_, Dec 13 2021 %E A309260 a(9) confirmed by _Vaclav Kotesovec_, Dec 18 2021 %E A309260 a(10)-a(11) from _Bert Dobbelaere_, Oct 24 2022