a(n) = A027052(n, 2n-5).

Terms

a(0) =0a(1) =2a(2) =6a(3) =20a(4) =66a(5) =210a(6) =652a(7) =1988a(8) =5982a(9) =17830a(10) =52782a(11) =155480a(12) =456364a(13) =1336066a(14) =3904280a(15) =11394244a(16) =33222902a(17) =96812174a(18) =282009512a(19) =821327088a(20) =2391918708a(21) =6966267782a(22) =20291422370a(23) =59116724728a(24) =172271893036a(25) =502157965938