a(n) = smallest number which is not the sum of exactly 1 or a(n-1) earlier terms.

Terms

a(0) =1a(1) =2a(2) =5a(3) =3a(4) =14a(5) =4a(6) =39a(7) =6a(8) =119a(9) =7a(10) =352a(11) =8a(12) =706a(13) =9a(14) =2104a(15) =10a(16) =4209a(17) =11a(18) =8419a(19) =12a(20) =24552a(21) =13a(22) =49106a(23) =15a(24) =188594a(25) =16a(26) =524494a(27) =17a(28) =1933822a(29) =18