Numbers k which when sandwiched between two 9's give a multiple of k.

Terms

a(0) =1a(1) =3a(2) =9a(3) =11a(4) =13a(5) =21a(6) =33a(7) =39a(8) =63a(9) =77a(10) =91a(11) =99a(12) =137a(13) =219a(14) =411a(15) =657a(16) =9091a(17) =29703a(18) =89109a(19) =909091a(20) =5882353a(21) =10989011a(22) =12145749a(23) =12987013a(24) =14354067a(25) =20979021a(26) =22556391a(27) =32967033a(28) =36437247a(29) =38961039