A137749 - cp's OEIS frontend

A137749 Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.

%I A137749 #5 Jun 29 2025 22:19:02
%S A137749 1,30,13560,27785520,162030637440,2156625389318400,
%T A137749 56857271240920550400,2686506065987036477184000,
%U A137749 211180868835057744408834048000,26072812428113877344085395644416000,4829206317935252350431489703482654720000
%N A137749 Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.
%F A137749 a(n) = ((2n)!^3 / n!^2 / 2^(2n) + (2n)!) / (4n).
%F A137749 a(n) = A137737(2n)
%Y A137749 Cf. A114938, A137729, A137730, A137737
%K A137749 nonn
%O A137749 1,2
%A A137749 _Max Alekseyev_, Feb 09 2008

cp's OEIS Frontend

A137749 Number of circular permutations of the multiset {1,1,2,2,...,2n,2n} (up to rotations) with even distances between equal elements.