a(0)=0, a(1)=1; for n>1, a(n) = 6*a(n-1)-4*a(n-2).

Terms

a(0) =0a(1) =1a(2) =6a(3) =32a(4) =168a(5) =880a(6) =4608a(7) =24128a(8) =126336a(9) =661504a(10) =3463680a(11) =18136064a(12) =94961664a(13) =497225728a(14) =2603507712a(15) =13632143360a(16) =71378829312a(17) =373744402432