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 A320334 #17 Oct 15 2018 07:43:29
%S A320334 1,1,0,3,12,25,0,475,5352,17157,0,896535,15083680,68879713,0
%N A320334 Number of ways to group the first 2*n positive integers into n pairs (xi, yi) with xi < yi, and such that the n numbers (yi - xi) mod n are all different.
%C A320334 A variant of A060963, a(n) <= A060963(n) by definition.
%H A320334 Rémy Sigrist, <a href="/A320334/a320334.txt">C++ program for A320334</a>
%e A320334 a(3) = 3 because {(1,4), (2,6), (3,5)}, {(1,5), (2,4), (3,6)}, {(1,6), (2,5), (3,4)} are corresponding sets.
%o A320334 (C++) See Links section.
%Y A320334 Cf. A060963, A320168, A320333.
%K A320334 nonn,more
%O A320334 0,4
%A A320334 _Altug Alkan_, Oct 11 2018
%E A320334 Terms computed by _Rémy Sigrist_, Oct 11 2018