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 A118668 #9 Jul 11 2015 08:20:07
%S A118668 1,1,1,1,2,2,2,2,2,2,1,1,2,2,3,3,3,3,2,3,3,3,3,3,2,3,3,3,3,3,3,3,3,3,
%T A118668 2,3,1,3,3,3,3,3,3,3,2,4,3,3,3,3,4,4,4,3,4,4,4,4,2,3,4,3,4,4,3,4,2,3,
%U A118668 4,4,4,3,3,4,3,4,3,2,4,4,4,3,3,4,4,3,4,3,4,3,4,4,4,4,3,4,3,4,4,4,2,2,3,3,4
%N A118668 Number of distinct digits needed to write the n-th triangular number in decimal representation.
%C A118668 0 < a(n) <= 10;
%C A118668 a(n) = A043537(A000217(n)).
%H A118668 Reinhard Zumkeller, <a href="/A118668/b118668.txt">Table of n, a(n) for n = 0..10000</a>
%e A118668 n=99: 99*(99+1)/2 = 4950 -> a(99) = #{0,4,5,9} = 4;
%e A118668 see A119033 for an overview of sequences with terms composed of not more than 3 distinct digits.
%e A118668 n=100: 100*(100+1)/2 = 5050 -> a(100) = #{0,5} = 2;
%t A118668 Length[Union[IntegerDigits[#]]]&/@Accumulate[Range[0,110]] (* _Harvey P. Dale_, Jul 23 2012 *)
%o A118668 (Haskell)
%o A118668 a118668 = a043537 . a000217
%o A118668 a118668_list = map a043537 a000217_list
%o A118668 -- _Reinhard Zumkeller_, Jul 11 2015
%Y A118668 Cf. A000217, A043537, A045914, A213517, A213518, A255678.
%K A118668 nonn,base
%O A118668 0,5
%A A118668 _Reinhard Zumkeller_, May 19 2006