a(1)=3, a(2)=2, a(n)=3*a(n-1) + 2*a(n-2).

Terms

a(0) =3a(1) =2a(2) =12a(3) =40a(4) =144a(5) =512a(6) =1824a(7) =6496a(8) =23136a(9) =82400a(10) =293472a(11) =1045216a(12) =3722592a(13) =13258208a(14) =47219808a(15) =168175840a(16) =598967136a(17) =2133253088a(18) =7597693536a(19) =27059586784a(20) =96374147424a(21) =343241615840