a(1) = 2, a(2) = 3; thereafter a(n) is the sum of all the previous terms.

Terms

a(0) =2a(1) =3a(2) =5a(3) =10a(4) =20a(5) =40a(6) =80a(7) =160a(8) =320a(9) =640a(10) =1280a(11) =2560a(12) =5120a(13) =10240a(14) =20480a(15) =40960a(16) =81920a(17) =163840a(18) =327680a(19) =655360a(20) =1310720a(21) =2621440a(22) =5242880a(23) =10485760a(24) =20971520a(25) =41943040a(26) =83886080a(27) =167772160a(28) =335544320a(29) =671088640