Numbers k such that 6 and 7 occur juxtaposed in the base-10 representation of k but not of k-1.

Terms

a(0) =67a(1) =76a(2) =167a(3) =176a(4) =267a(5) =276a(6) =367a(7) =376a(8) =467a(9) =476a(10) =567a(11) =576a(12) =667a(13) =670a(14) =760a(15) =776a(16) =867a(17) =876a(18) =967a(19) =976a(20) =1067a(21) =1076a(22) =1167a(23) =1176a(24) =1267a(25) =1276a(26) =1367a(27) =1376a(28) =1467a(29) =1476