(n^2)*(n^2-1)*(n^2-2)*(n^2-3).

Terms

a(0) =0a(1) =0a(2) =24a(3) =3024a(4) =43680a(5) =303600a(6) =1413720a(7) =5085024a(8) =15249024a(9) =39929760a(10) =94109400a(11) =203889840a(12) =412293024a(13) =787083024a(14) =1431033240a(15) =2495102400a(16) =4195023360a(17) =6831849024a(18) =10817040024a(19) =16702719120a(20) =25217757600a(21) =37310399280a(22) =54198168024a(23) =77425845024a(24) =108932342400