Number of modes of connections of 2n points.

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =46a(5) =207a(6) =979a(7) =4797a(8) =24138a(9) =123998a(10) =647615a(11) =3428493a(12) =18356714a(13) =99229015a(14) =540807165a(15) =2968468275a(16) =16395456762a(17) =91053897066a(18) =508151297602