Numbers containing only digits 3 or 7 in decimal representation.

Terms

a(0) =3a(1) =7a(2) =33a(3) =37a(4) =73a(5) =77a(6) =333a(7) =337a(8) =373a(9) =377a(10) =733a(11) =737a(12) =773a(13) =777a(14) =3333a(15) =3337a(16) =3373a(17) =3377a(18) =3733a(19) =3737a(20) =3773a(21) =3777a(22) =7333a(23) =7337a(24) =7373a(25) =7377a(26) =7733a(27) =7737a(28) =7773a(29) =7777