Triple factorials n!!!: a(n) = n*a(n-3).

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =4a(5) =5a(6) =18a(7) =28a(8) =40a(9) =162a(10) =280a(11) =440a(12) =1944a(13) =3640a(14) =6160a(15) =29160a(16) =58240a(17) =104720a(18) =524880a(19) =1106560a(20) =2094400a(21) =11022480a(22) =24344320a(23) =48171200a(24) =264539520a(25) =608608000a(26) =1252451200a(27) =7142567040a(28) =17041024000a(29) =36321084800