a(n) least k > a(n-1) such that a(k)=s(n), for n >= 2, where s = A026600.

Terms

a(0) =1a(1) =6a(2) =9a(3) =11a(4) =15a(5) =18a(6) =20a(7) =24a(8) =27a(9) =28a(10) =33a(11) =36a(12) =38a(13) =42a(14) =45a(15) =47a(16) =51a(17) =54a(18) =55a(19) =60a(20) =63a(21) =65a(22) =69a(23) =72a(24) =74a(25) =78a(26) =81a(27) =84a(28) =87a(29) =90