a(n) = least k such that s(k) = n, where s = A026280.

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =8a(6) =10a(7) =12a(8) =13a(9) =15a(10) =16a(11) =18a(12) =19a(13) =21a(14) =22a(15) =24a(16) =26a(17) =27a(18) =29a(19) =31a(20) =32a(21) =34a(22) =36a(23) =37a(24) =39a(25) =41a(26) =42a(27) =44a(28) =45a(29) =47