This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A125098 #13 Dec 10 2015 04:45:41
%S A125098 0,1,10,11,12,100,101,102,110,111,112,120,121,122,123,1000,1001,1002,
%T A125098 1010,1011,1012,1020,1021,1022,1023,1100,1101,1102,1110,1111,1112,
%U A125098 1120,1121,1122,1123,1200,1201,1202,1203,1210,1211,1212,1213,1220,1221,1222
%N A125098 Values occurring in A123895.
%C A125098 Also, numbers n such that A123895(n) = n. Each digit is either 0, has occurred before, or is one more than the largest preceding digit. The number of k-digit numbers in this sequence is A005493(k-1) for 2<=k<=9. The initial 0 prevents a match for k=1; later values fall short because there are no digits beyond 9 available in decimal.
%H A125098 R. J. Mathar, <a href="/A125098/b125098.txt">Table of n, a(n) for n = 0..876</a>
%p A125098 bag := {} ;
%p A125098 for i from 0 to 99999 do
%p A125098 bag := bag union {A123895(i)} ;
%p A125098 end do:
%p A125098 sort(convert(bag,list)) ; # _R. J. Mathar_, Dec 10 2015
%t A125098 f[n_] := Block[{d = Prepend[IntegerDigits@ n, 0], a, b, w}, b = DeleteDuplicates@ d; a = Range[0, Length@ b]; w = FromDigits@ Flatten[Part[a, FirstPosition[b, #]] & /@ d]; w]; Union@ Table[f@n, {n, 0, 10^4}] (* _Michael De Vlieger_, Dec 09 2015, Version 10 *)
%Y A125098 Cf. A123895, A005493, A123902.
%K A125098 base,easy,nonn
%O A125098 0,3
%A A125098 _Franklin T. Adams-Watters_, Nov 20 2006