a(n) = T(n,n-2), array T as in A055450.

Terms

a(0) =1a(1) =3a(2) =5a(3) =19a(4) =75a(5) =305a(6) =1270a(7) =5390a(8) =23236a(9) =101480a(10) =448085a(11) =1997115a(12) =8973255a(13) =40602093a(14) =184853055a(15) =846206025a(16) =3892585325a(17) =17984308775a(18) =83417287855a(19) =388297304825