a(n) = least k such that s(k) = n, where s = A026276.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =7a(5) =9a(6) =10a(7) =12a(8) =13a(9) =15a(10) =16a(11) =18a(12) =20a(13) =21a(14) =23a(15) =25a(16) =26a(17) =28a(18) =30a(19) =31a(20) =33a(21) =34a(22) =36a(23) =38a(24) =39a(25) =41a(26) =42a(27) =44a(28) =46a(29) =47