a(n) = n*(n-1)*(n-3)*(n-5).

Terms

a(0) =0a(1) =0a(2) =6a(3) =0a(4) =-12a(5) =0a(6) =90a(7) =336a(8) =840a(9) =1728a(10) =3150a(11) =5280a(12) =8316a(13) =12480a(14) =18018a(15) =25200a(16) =34320a(17) =45696a(18) =59670a(19) =76608a(20) =96900a(21) =120960a(22) =149226a(23) =182160a(24) =220248a(25) =264000a(26) =313950a(27) =370656a(28) =434700a(29) =506688