Numbers n such that string 5,6 occurs in the base 10 representation of n but not of n-1.

Terms

a(0) =56a(1) =156a(2) =256a(3) =356a(4) =456a(5) =556a(6) =560a(7) =656a(8) =756a(9) =856a(10) =956a(11) =1056a(12) =1156a(13) =1256a(14) =1356a(15) =1456a(16) =1556a(17) =1560a(18) =1656a(19) =1756a(20) =1856a(21) =1956a(22) =2056a(23) =2156a(24) =2256a(25) =2356a(26) =2456a(27) =2556a(28) =2560a(29) =2656