a(n) is the numerator of Product_{i=0..n-1} (n-i)^((-1)^ceiling(i/2)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =2a(4) =5a(5) =9a(6) =7a(7) =40a(8) =45a(9) =7a(10) =308a(11) =48a(12) =975a(13) =539a(14) =88a(15) =1664a(16) =1105a(17) =24255a(18) =13376a(19) =56576a(20) =41769a(21) =48279a(22) =55936a(23) =226304a(24) =348075a(25) =370139a(26) =671232a(27) =870400a(28) =2082925a(29) =4283037