Numbers k such that 5 and 6 occur juxtaposed in the base-10 representation of k but not of k+1.

Terms

a(0) =56a(1) =65a(2) =156a(3) =165a(4) =256a(5) =265a(6) =356a(7) =365a(8) =456a(9) =465a(10) =556a(11) =569a(12) =659a(13) =665a(14) =756a(15) =765a(16) =856a(17) =865a(18) =956a(19) =965a(20) =1056a(21) =1065a(22) =1156a(23) =1165a(24) =1256a(25) =1265a(26) =1356a(27) =1365a(28) =1456a(29) =1465