a(n) = (n-1)*(n-2)*(n-3)*(3*n-10)*3^(n-5)/4.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =30a(5) =360a(6) =2970a(7) =19845a(8) =115668a(9) =612360a(10) =3018060a(11) =14073345a(12) =62788770a(13) =270208224a(14) =1128426390a(15) =4594307445a(16) =18302828040a(17) =71553216240a(18) =275154640632