Number of ménage permutations.

Terms

a(0) =1a(1) =2a(2) =5a(3) =20a(4) =87a(5) =616a(6) =4843a(7) =44128a(8) =444621a(9) =4936274a(10) =59661265a(11) =780547332a(12) =10987097799a(13) =165587196328