Floor(Gamma(n/3)).

Terms

a(0) =2a(1) =1a(2) =1a(3) =0a(4) =0a(5) =1a(6) =1a(7) =1a(8) =2a(9) =2a(10) =4a(11) =6a(12) =9a(13) =14a(14) =24a(15) =40a(16) =68a(17) =120a(18) =214a(19) =389a(20) =720a(21) =1355a(22) =2593a(23) =5040a(24) =9940a(25) =19884a(26) =40320a(27) =82834a(28) =172328a(29) =362880