Numbers k such that 7 and 8 occur juxtaposed in the base-10 representation of k but not of k+1.

Terms

a(0) =78a(1) =87a(2) =178a(3) =187a(4) =278a(5) =287a(6) =378a(7) =387a(8) =478a(9) =487a(10) =578a(11) =587a(12) =678a(13) =687a(14) =778a(15) =789a(16) =879a(17) =887a(18) =978a(19) =987a(20) =1078a(21) =1087a(22) =1178a(23) =1187a(24) =1278a(25) =1287a(26) =1378a(27) =1387a(28) =1478a(29) =1487