Numbers having only digits 1 and 3 in their decimal representation.

Terms

a(0) =1a(1) =3a(2) =11a(3) =13a(4) =31a(5) =33a(6) =111a(7) =113a(8) =131a(9) =133a(10) =311a(11) =313a(12) =331a(13) =333a(14) =1111a(15) =1113a(16) =1131a(17) =1133a(18) =1311a(19) =1313a(20) =1331a(21) =1333a(22) =3111a(23) =3113a(24) =3131a(25) =3133a(26) =3311a(27) =3313a(28) =3331a(29) =3333