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

Terms

a(0) =5a(1) =7a(2) =9a(3) =11a(4) =14a(5) =17a(6) =20a(7) =23a(8) =25a(9) =28a(10) =30a(11) =33a(12) =35a(13) =38a(14) =40a(15) =43a(16) =46a(17) =48a(18) =51a(19) =54a(20) =56a(21) =59a(22) =62a(23) =64a(24) =67a(25) =70a(26) =72a(27) =75a(28) =77a(29) =80