Smallest integer not the sum of powers of some earlier terms.

Terms

a(0) =1a(1) =2a(2) =6a(3) =12a(4) =25a(5) =85a(6) =194a(7) =590a(8) =1695a(9) =4879a(10) =19077a(11) =83994a(12) =167988a(13) =1041780a(14) =2448645a(15) =9677725a(16) =33250403a(17) =117499773a(18) =811972692a(19) =1762911460