Number of non-isomorphic graphs on 4n vertices whose edges are the union of two n-edge matchings.

Terms

a(0) =1a(1) =3a(2) =9a(3) =23a(4) =54a(5) =118a(6) =246a(7) =489a(8) =940a(9) =1751a(10) =3177a(11) =5630a(12) =9776a(13) =16659a(14) =27922a(15) =46092a(16) =75039a(17) =120615a(18) =191611a(19) =301086a(20) =468342a(21) =721638a(22) =1102113a(23) =1669226a(24) =2508429a(25) =3741741a(26) =5542532a(27) =8155720a(28) =11925654a(29) =17334077