a(n) = A324484(n)/n.

Terms

a(0) =1a(1) =0a(2) =5a(3) =6a(4) =24a(5) =40a(6) =120a(7) =250a(8) =640a(9) =1452a(10) =3600a(11) =8510a(12) =20880a(13) =50460a(14) =124024a(15) =303750a(16) =750120a(17) =1853120a(18) =4600200a(19) =11437548a(20) =28527320a(21) =71281800a(22) =178526880a(23) =447893250a(24) =1125750120a(25) =2833844040a(26) =7144449920a(27) =18036271740a(28) =45591631800a(29) =115381449692