Scaled Chebyshev U-polynomial evaluated at sqrt(6)/2.

Terms

a(0) =1a(1) =6a(2) =30a(3) =144a(4) =684a(5) =3240a(6) =15336a(7) =72576a(8) =343440a(9) =1625184a(10) =7690464a(11) =36391680a(12) =172207296a(13) =814893696a(14) =3856118400a(15) =18247348224a(16) =86347378944a(17) =408600184320