a(n) = T(2n-1,n-2), T given by A027157.

Terms

a(0) =4a(1) =15a(2) =112a(3) =440a(4) =3328a(5) =13552a(6) =103168a(7) =429696a(8) =3282944a(9) =13882880a(10) =106307584a(11) =454471680a(12) =3485499392a(13) =15022878720a(14) =115345653760a(15) =500317061120