a(n) = 2^(n-4)*C(n,4).

Terms

a(0) =1a(1) =10a(2) =60a(3) =280a(4) =1120a(5) =4032a(6) =13440a(7) =42240a(8) =126720a(9) =366080a(10) =1025024a(11) =2795520a(12) =7454720a(13) =19496960a(14) =50135040a(15) =127008768a(16) =317521920a(17) =784465920a(18) =1917583360a(19) =4642570240a(20) =11142168576a(21) =26528972800a(22) =62704844800a(23) =147220070400