A bisection of A221075.

Terms

a(0) =12a(1) =24a(2) =192a(3) =360a(4) =2700a(5) =5040a(6) =37632a(7) =70224a(8) =524172a(9) =978120a(10) =7300800a(11) =13623480a(12) =101687052a(13) =189750624a(14) =1416317952a(15) =2642885280a(16) =19726764300a(17) =36810643320a(18) =274758382272a(19) =512706121224