a(n) = greatest k such that s(k) = n, where s = A026370.

Terms

a(0) =4a(1) =7a(2) =10a(3) =15a(4) =18a(5) =23a(6) =26a(7) =31a(8) =34a(9) =37a(10) =40a(11) =45a(12) =48a(13) =53a(14) =56a(15) =59a(16) =62a(17) =67a(18) =70a(19) =75a(20) =78a(21) =81a(22) =84a(23) =89a(24) =92a(25) =97a(26) =100a(27) =105a(28) =108a(29) =113