a(n) = A027170(2n, n-1).

Terms

a(0) =5a(1) =30a(2) =123a(3) =472a(4) =1790a(5) =6794a(6) =25879a(7) =98952a(8) =379674a(9) =1461248a(10) =5638930a(11) =21811540a(12) =84542016a(13) =328287506a(14) =1276868111a(15) =4973645576a(16) =19398954626a(17) =75753497816a(18) =296142817406