a(n) = A006967(n)/2.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =12a(5) =16a(6) =20a(7) =60a(8) =148a(9) =324a(10) =664a(11) =1600a(12) =4956a(13) =12796a(14) =27960a(15) =71596a(16) =255348a(17) =725648a(18) =1748672a(19) =5225912a(20) =19285352a(21) =59457496a(22) =157617936a(23) =507412376a(24) =1981842248a(25) =6583065076a(26) =18923150952a(27) =65253983544a(28) =266659315468a(29) =942275107988