a(n) = 2^(n-3)*(n+2)*(n+3)*(n+4)/3.

Terms

a(0) =1a(1) =5a(2) =20a(3) =70a(4) =224a(5) =672a(6) =1920a(7) =5280a(8) =14080a(9) =36608a(10) =93184a(11) =232960a(12) =573440a(13) =1392640a(14) =3342336a(15) =7938048a(16) =18677760a(17) =43581440a(18) =100925440a(19) =232128512a(20) =530579456a(21) =1205862400a(22) =2726297600a(23) =6134169600a(24) =13740539904a(25) =30651973632a(26) =68115496960