a(n) = least k such that s(k) = n, where s = A026284.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =5a(5) =7a(6) =9a(7) =11a(8) =13a(9) =15a(10) =16a(11) =18a(12) =19a(13) =21a(14) =22a(15) =24a(16) =25a(17) =27a(18) =28a(19) =30a(20) =32a(21) =33a(22) =35a(23) =37a(24) =38a(25) =40a(26) =42a(27) =43a(28) =45a(29) =47