%I #7 Jul 27 2019 11:08:00

%S 99,199,299,399,499,599,699,799,899,990,1099,1199,1299,1399,1499,1599,

%T 1699,1799,1899,1990,2099,2199,2299,2399,2499,2599,2699,2799,2899,

%U 2990,3099,3199,3299,3399,3499,3599,3699,3799,3899

%N Numbers n such that string 9,9 occurs in the base 10 representation of n but not of n-1.

%t SequencePosition[Table[If[SequenceCount[IntegerDigits[n],{9,9}]>0,1,0],{n,4000}],{0,1}][[All,2]] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jul 27 2019 *)

%K nonn,base

%O 1,1

%A _Clark Kimberling_