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A283871 For all n, the set consisting of the terms {a(1), a(2), a(3), ..., a(n)} has an even number of digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.

%I A283871 #22 Jan 07 2024 10:59:33
%S A283871 11,22,33,44,55,66,77,88,99,1001,1010,1100,1111,1122,1133,1144,1155,
%T A283871 1166,1177,1188,1199,1212,1221,1313,1331,1414,1441,1515,1551,1616,
%U A283871 1661,1717,1771,1818,1881,1919,1991,2002,2020,2112,2121,2200,2211,2222,2233,2244,2255,2266,2277,2288,2299,2323,2332,2424,2442,2525
%N A283871 For all n, the set consisting of the terms {a(1), a(2), a(3), ..., a(n)} has an even number of digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9.
%C A283871 The sequence is started with a(1) = 11 and always extended with the smallest integer not yet present and not leading to a contradiction.
%C A283871 Numbers that have an even number of each digit 0 to 9.  - _Robert Israel_, Jan 07 2024
%H A283871 Robert Israel, <a href="/A283871/b283871.txt">Table of n, a(n) for n = 1..10000</a>
%e A283871 The set consisting of the first 15 terms is {11, 22, 33, 44, 55, 66, 77, 88, 99, 1001, 1010, 1100, 1111, 1122, 1133}; we count there six 0's, sixteen 1's, four 2's, four 3's, etc. All those quantities of digits are even numbers.
%p A283871 filter:= proc(n) local L; L:= convert(n,base,10);
%p A283871    andmap(t -> numboccur(t,L)::even, L) end proc:
%p A283871 select(filter, [$1..10^4]); # _Robert Israel_, Jan 07 2024
%Y A283871 Cf. A283870.
%K A283871 nonn,base
%O A283871 1,1
%A A283871 _Eric Angelini_ and _Jean-Marc Falcoz_, Mar 17 2017