a(n) = Product_{k=1..n} floor((2*n+1)/k - 1).

Terms

a(0) =1a(1) =2a(2) =4a(3) =12a(4) =48a(5) =80a(6) =360a(7) =1344a(8) =2688a(9) =8640a(10) =51840a(11) =63360a(12) =443520a(13) =1198080a(14) =2515968a(15) =10886400a(16) =48384000a(17) =87736320a(18) =465315840a(19) =1134673920a(20) =3309465600a(21) =11887948800a(22) =71530905600a(23) =78343372800a(24) =528817766400