a(n) = 4*a(n-1) - 2*a(n-2) with a(0) = 1, a(1) = 4.

Terms

a(0) =1a(1) =4a(2) =14a(3) =48a(4) =164a(5) =560a(6) =1912a(7) =6528a(8) =22288a(9) =76096a(10) =259808a(11) =887040a(12) =3028544a(13) =10340096a(14) =35303296a(15) =120532992a(16) =411525376a(17) =1405035520a(18) =4797091328a(19) =16378294272a(20) =55918994432a(21) =190919389184a(22) =651839567872