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

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =864a(5) =17280a(6) =144000a(7) =756000a(8) =2963520a(9) =9483264a(10) =26127360a(11) =64152000a(12) =143748000a(13) =298995840a(14) =584648064a(15) =1085142240a(16) =1926288000a(17) =3290112000a(18) =5433384960a(19) =8710395264a(20) =13600573920a(21) =20741616000a(22) =30968784000a(23) =45361118880a(24) =65295324864a(25) =92508134400a(26) =129168000000