First diagonal of A027517.

Terms

a(0) =1a(1) =1a(2) =4a(3) =9a(4) =450a(5) =14700a(6) =23716a(7) =11025a(8) =5929a(9) =3025a(10) =27225a(11) =14400a(12) =42688800a(13) =3870830656a(14) =9109748025a(15) =5288198400a(16) =1599516800a(17) =1903751424a(18) =57588480576