a(n) is the concatenation of n and 5n.

Terms

a(0) =15a(1) =210a(2) =315a(3) =420a(4) =525a(5) =630a(6) =735a(7) =840a(8) =945a(9) =1050a(10) =1155a(11) =1260a(12) =1365a(13) =1470a(14) =1575a(15) =1680a(16) =1785a(17) =1890a(18) =1995a(19) =20100a(20) =21105a(21) =22110a(22) =23115a(23) =24120a(24) =25125a(25) =26130a(26) =27135a(27) =28140a(28) =29145a(29) =30150