A217214(n)/2.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =19a(5) =161a(6) =1056a(7) =6105a(8) =32747a(9) =167167a(10) =823888a(11) =3955458a(12) =18608030a(13) =86131826a(14) =393439840a(15) =1777499685a(16) =7956046035a(17) =35328205275a(18) =155792097120a(19) =682880049390