Numbers having four 7's in base 10.

Terms

a(0) =7777a(1) =17777a(2) =27777a(3) =37777a(4) =47777a(5) =57777a(6) =67777a(7) =70777a(8) =71777a(9) =72777a(10) =73777a(11) =74777a(12) =75777a(13) =76777a(14) =77077a(15) =77177a(16) =77277a(17) =77377a(18) =77477a(19) =77577a(20) =77677a(21) =77707a(22) =77717a(23) =77727a(24) =77737a(25) =77747a(26) =77757a(27) =77767a(28) =77770a(29) =77771