Numbers n such that string 7,7 occurs in the base 10 representation of n but not of n-1.

Terms

a(0) =77a(1) =177a(2) =277a(3) =377a(4) =477a(5) =577a(6) =677a(7) =770a(8) =877a(9) =977a(10) =1077a(11) =1177a(12) =1277a(13) =1377a(14) =1477a(15) =1577a(16) =1677a(17) =1770a(18) =1877a(19) =1977a(20) =2077a(21) =2177a(22) =2277a(23) =2377a(24) =2477a(25) =2577a(26) =2677a(27) =2770a(28) =2877a(29) =2977