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

Terms

a(0) =6a(1) =8a(2) =10a(3) =12a(4) =14a(5) =17a(6) =20a(7) =23a(8) =26a(9) =29a(10) =31a(11) =34a(12) =36a(13) =39a(14) =41a(15) =44a(16) =46a(17) =49a(18) =51a(19) =54a(20) =57a(21) =59a(22) =62a(23) =65a(24) =67a(25) =70a(26) =73a(27) =75a(28) =78a(29) =81