a(n) = least k such that s(k) = n, where s = A026272.

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =7a(5) =9a(6) =10a(7) =12a(8) =14a(9) =15a(10) =17a(11) =19a(12) =20a(13) =22a(14) =23a(15) =25a(16) =27a(17) =28a(18) =30a(19) =31a(20) =33a(21) =35a(22) =36a(23) =38a(24) =40a(25) =41a(26) =43a(27) =44a(28) =46a(29) =48