a(1) = 4; a(n) = smallest composite number greater than the sum of all previous terms.

Terms

a(0) =4a(1) =6a(2) =12a(3) =24a(4) =48a(5) =95a(6) =190a(7) =380a(8) =760a(9) =1520a(10) =3040a(11) =6080a(12) =12160a(13) =24320a(14) =48640a(15) =97280a(16) =194560a(17) =389120a(18) =778240a(19) =1556480a(20) =3112960a(21) =6225920a(22) =12451840a(23) =24903680a(24) =49807360a(25) =99614720a(26) =199229440a(27) =398458880a(28) =796917760a(29) =1593835520