Ceiling(Gamma(n/3)).

Terms

a(0) =3a(1) =2a(2) =1a(3) =1a(4) =1a(5) =1a(6) =2a(7) =2a(8) =2a(9) =3a(10) =5a(11) =6a(12) =10a(13) =15a(14) =24a(15) =41a(16) =69a(17) =120a(18) =215a(19) =390a(20) =720a(21) =1356a(22) =2594a(23) =5040a(24) =9941a(25) =19885a(26) =40320a(27) =82835a(28) =172329a(29) =362880