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A210419 List the positions of all digits 5 in the concatenation of all terms, not necessarily in order. This is the lexicographically earliest such sequence.

%I A210419 #21 Apr 18 2021 02:14:59
%S A210419 2,5,4,55,7,50,11,51,15,52,14,21,53,25,54,24,31,56,35,57,34,41,58,45,
%T A210419 59,44,65,555,5555,550,63,505,68,500,73,501,78,502,83,503,88,504,93,
%U A210419 506,98,507,104,508,110,509,115,119,510,125,511,124,134,512,140,513
%N A210419 List the positions of all digits 5 in the concatenation of all terms, not necessarily in order. This is the lexicographically earliest such sequence.
%C A210419 See A210415 for comments, links, and code.
%H A210419 Danny Rorabaugh, <a href="/A210419/b210419.txt">Table of n, a(n) for n = 1..1000</a>
%e A210419 The sequence cannot start with 1 because the first digit is not 5. Let us start with 2: the second digit is equal to 5. The third digit cannot be 3 because the third digit is not 5. So let it be 4. The next term must begin with a 5 because 4 is already in the sequence. Since 5 is also a previous term, it must be 55. With 2,4,5 already used, and 1,3,6 pointing at digits that are not 5, the next term must be 7.
%Y A210419 Cf. A210414, A210415, A210416, A210417, A210418, A210420, A210421, A210422, A210423.
%K A210419 nonn,base
%O A210419 1,1
%A A210419 _Paolo P. Lava_, Mar 26 2012
%E A210419 a(5)-a(90) corrected by _Danny Rorabaugh_, Nov 27 2015