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 A137729 #10 Jul 01 2025 16:04:51
%S A137729 1,1,2,16,318,11352,623760,48648960,5108105520,694702028160,
%T A137729 118794043549440,24946749109094400,6311527524161798400,
%U A137729 1893458257242791500800,664603848292138865510400,269829162406607158901145600
%N A137729 Number of circular permutations of the multiset {1,1,2,2,...,n,n} (up to rotations).
%H A137729 Alois P. Heinz, <a href="/A137729/b137729.txt">Table of n, a(n) for n = 0..200</a>
%F A137729 a(n) = ((2*n)!/2^n + n!) / (2*n).
%Y A137729 Cf. A114938, A137730, A137737, A137749.
%Y A137729 Row n=2 of A208183.
%K A137729 nonn
%O A137729 0,3
%A A137729 _Max Alekseyev_, Feb 09 2008
%E A137729 a(0)=1 prepended by _Alois P. Heinz_, Jul 28 2015