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 A321797 #9 Nov 21 2018 03:20:36
%S A321797 0,0,0,0,0,0,0,0,0,0,0,11,0,0,0,0,0,0,0,0,0,0,22,0,0,0,0,0,0,0,0,0,0,
%T A321797 33,0,0,0,0,0,0,0,0,0,0,44,0,0,0,0,0,0,0,0,0,0,55,0,0,0,0,0,0,0,0,0,0,
%U A321797 66,0,0,0,0,0,0,0,0,0,0,77,0,0,0,0,0,0,0,0,0,0,88,0,0,0,0,0,0,0,0,0,0,99,0,11,0,0,0,0,0,0,0,0,11,111,11,11,11,11,11,11,11,11,0,11,22,0,0,0,0,0,0,0,0,11,0,33,0,0,0,0,0,0,0,11,0,0,44,0,0,0,0,0,0,11,0,0,0,55,0,0,0,0,0,11,0,0,0,0,66,0,0,0,0,11,0,0,0,0,0,77,0,0,0,11,0,0,0,0,0,0,88,0,0,11,0,0,0,0,0,0,0,99
%N A321797 Delete the decimal digits of n that appear exactly once; write 0 if all digits disappear.
%C A321797 A companion sequence to A320486.
%C A321797 Digits that appear exactly once in n are erased. Leading zeros are erased unless the result is 0. If all digits are erased, we write 0 for the result (A321800 is another version, which uses -1 for the empty string).
%C A321797 More than the usual number of terms are shown in order to reach some interesting examples.
%H A321797 Chai Wah Wu, <a href="/A321797/b321797.txt">Table of n, a(n) for n = 0..10000</a>
%e A321797 12321 becomes 1221, 1123 becomes 11, 11231 becomes 111, and 100223 becomes 22 (as we don't accept leading zeros). Note that 12345 disappears immediately and we get 0.
%o A321797 (Python)
%o A321797 def A321797(n):
%o A321797 return int('0'+''.join(d if str(n).count(d) != 1 else '' for d in str(n)))
%Y A321797 Cf. A320486, A321800.
%K A321797 nonn,base
%O A321797 0,12
%A A321797 _Chai Wah Wu_, Nov 19 2018