Repdigit numbers, or numbers whose digits are all equal.

Terms

a(0) =0a(1) =1a(2) =2a(3) =3a(4) =4a(5) =5a(6) =6a(7) =7a(8) =8a(9) =9a(10) =11a(11) =22a(12) =33a(13) =44a(14) =55a(15) =66a(16) =77a(17) =88a(18) =99a(19) =111a(20) =222a(21) =333a(22) =444a(23) =555a(24) =666a(25) =777a(26) =888a(27) =999a(28) =1111a(29) =2222