Numbers k which when sandwiched between two 6's give a multiple of k.

Terms

a(0) =1a(1) =2a(2) =3a(3) =6a(4) =11a(5) =13a(6) =14a(7) =21a(8) =22a(9) =26a(10) =33a(11) =39a(12) =42a(13) =66a(14) =77a(15) =78a(16) =91a(17) =137a(18) =146a(19) =219a(20) =274a(21) =411a(22) =438a(23) =822a(24) =9091a(25) =19802a(26) =29703a(27) =59406a(28) =909091a(29) =5882353