Number of positive clusters of type D_n.

Terms

a(0) =-1a(1) =1a(2) =5a(3) =20a(4) =77a(5) =294a(6) =1122a(7) =4290a(8) =16445a(9) =63206a(10) =243542a(11) =940576a(12) =3640210a(13) =14115100a(14) =54826020a(15) =213286590a(16) =830905245a(17) =3241119750a(18) =12657425550a(19) =49483369320a(20) =193641552390a(21) =758454277620