Numbers k such that the concatenation 1,2,3,... up to (k-1) is one less than a multiple of k.

Terms

a(0) =1a(1) =2a(2) =4a(3) =5a(4) =8a(5) =10a(6) =13a(7) =20a(8) =25a(9) =40a(10) =50a(11) =52a(12) =100a(13) =125a(14) =200a(15) =250a(16) =400a(17) =475a(18) =500a(19) =601a(20) =848a(21) =908a(22) =1000a(23) =1120a(24) =1250a(25) =1750a(26) =2000a(27) =2500a(28) =2800a(29) =2900