Numbers with all digits equal and from the set {1, 3, 7, 9}.

Terms

a(0) =1a(1) =3a(2) =7a(3) =9a(4) =11a(5) =33a(6) =77a(7) =99a(8) =111a(9) =333a(10) =777a(11) =999a(12) =1111a(13) =3333a(14) =7777a(15) =9999a(16) =11111a(17) =33333a(18) =77777a(19) =99999a(20) =111111a(21) =333333a(22) =777777a(23) =999999a(24) =1111111a(25) =3333333a(26) =7777777a(27) =9999999a(28) =11111111a(29) =33333333