Second row of A113439.

Terms

a(0) =1a(1) =3a(2) =12a(3) =50a(4) =212a(5) =905a(6) =3872a(7) =16576a(8) =70968a(9) =303832a(10) =1300737a(11) =5568473a(12) =23838453a(13) =102051167a(14) =436874885a(15) =1870233780a(16) =8006350999a(17) =34274673894a(18) =146727674181a(19) =628131735844