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

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =16a(5) =44a(6) =120a(7) =328a(8) =896a(9) =2448a(10) =6688a(11) =18272a(12) =49920a(13) =136384a(14) =372608a(15) =1017984a(16) =2781184a(17) =7598336a(18) =20759040a(19) =56714752a(20) =154947584a(21) =423324672a(22) =1156544512a(23) =3159738368a(24) =8632565760a(25) =23584608256a(26) =64434348032a(27) =176037912576a(28) =480944521216