a(n) = 2*a(n-1) + 2*a(n-2) for n > 2, a(0)=1, a(1)=1, a(2)=3.

Terms

a(0) =1a(1) =1a(2) =3a(3) =8a(4) =22a(5) =60a(6) =164a(7) =448a(8) =1224a(9) =3344a(10) =9136a(11) =24960a(12) =68192a(13) =186304a(14) =508992a(15) =1390592a(16) =3799168a(17) =10379520a(18) =28357376a(19) =77473792a(20) =211662336a(21) =578272256a(22) =1579869184a(23) =4316282880a(24) =11792304128a(25) =32217174016a(26) =88018956288a(27) =240472260608a(28) =656982433792