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

Terms

a(0) =1a(1) =2a(2) =8a(3) =24a(4) =80a(5) =256a(6) =832a(7) =2688a(8) =8704a(9) =28160a(10) =91136a(11) =294912a(12) =954368a(13) =3088384a(14) =9994240a(15) =32342016a(16) =104660992a(17) =338690048a(18) =1096024064a(19) =3546808320a(20) =11477712896a(21) =37142659072a(22) =120196169728a(23) =388962975744