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 A065004 #20 Aug 15 2021 15:15:31
%S A065004 1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111,
%T A065004 1100100,10201,1210,400,244,202,144,121,100,91,84,79,72,-1,64,-1,-1,
%U A065004 55,50,-1,-1,48,44,40,-1,-1,-1,-1,-1,37,34,31,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,28,26,24,22,20,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,19,18,17,16,15,14,13,12,11,10
%N A065004 100 written in base n, or -1 if the representation requires digits outside of 0 to 9.
%C A065004 The term 111....1111 should officially be called the "unary expansion", since in base 1 only the digit 0 may appear.
%C A065004 Terms exist for some bases up to 100. - _T. D. Noe_, Mar 09 2012
%t A065004 Table[s = IntegerDigits[100, n]; If[Max[s] > 9, -1, FromDigits[s]], {n, 2, 100}] (* _T. D. Noe_, Mar 09 2012 *)
%Y A065004 Cf. A065147, A208090 (100 in base -n).
%K A065004 base,less,sign,fini,full
%O A065004 1,1
%A A065004 _Bodo Zinser_, Nov 19 2001
%E A065004 Extended by _T. D. Noe_, Mar 09 2012
%E A065004 Title clarified by _Sean A. Irvine_, Aug 15 2021