a(1) = 1, a(2) = 2, a(3) = 5, a(4) = 8 and a(5) = 15, a(n) = Sum_{j=1..n-1} a(j).

Terms

a(0) =1a(1) =2a(2) =5a(3) =8a(4) =15a(5) =31a(6) =62a(7) =124a(8) =248a(9) =496a(10) =992a(11) =1984a(12) =3968a(13) =7936a(14) =15872a(15) =31744a(16) =63488a(17) =126976a(18) =253952a(19) =507904a(20) =1015808a(21) =2031616a(22) =4063232a(23) =8126464a(24) =16252928a(25) =32505856a(26) =65011712a(27) =130023424a(28) =260046848a(29) =520093696