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 A303785 Lexicographically earliest sequence of distinct terms such that what emerges from the mask is odd (see the Comment section for the mask explanation). 6

%I

%S 1,11,2,13,3,15,4,17,5,19,6,21,7,23,8,25,9,27,101,10,103,12,105,14,

%T 107,16,109,18,111,20,113,22,115,24,117,26,119,28,121,29,123,30,125,

%U 31,127,32,129,33,131,34,133,35,135,36,137,37,139,38,141,39,143,40,145,41,147,42,149,43,151,44,153,45,155,46,157,47

%N Lexicographically earliest sequence of distinct terms such that what emerges from the mask is odd (see the Comment section for the mask explanation).

%C For any pair of contiguous terms, one of the terms uses fewer digits than the other. This term is called the mask. Put the mask on the other term, starting from the left. What is not covered by the mask forms an odd number.

%C The sequence starts with a(1) = 1 and is always extended with the smallest integer not yet present that doesn't lead to a contradiction.

%C This sequence is a permutation of the integers > 0, as all integers will appear at some point, either as mask or masked.

%H Jean-Marc Falcoz, <a href="/A303785/b303785.txt">Table of n, a(n) for n = 1..10001</a>

%e In the pair (1,11), 1 is the mask; 1 emerges and is odd;

%e In the pair (11,2), 2 is the mask; 1 emerges and is odd;

%e In the pair (2,13), 2 is the mask; 3 emerges and is odd;

%e In the pair (13,3), 3 is the mask; 3 emerges and is odd;

%e ...

%e In the pair (11019,2018), 2018 is the mask; 9 emerges and is odd;

%e etc.

%Y Cf. A303782 (same idea with primes), A303783 (with squares), A303784 (with even numbers), A303786 (rebuilds the sequence itself term by term).

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _Jean-Marc Falcoz_, Apr 30 2018

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Last modified April 7 15:56 EDT 2020. Contains 333306 sequences. (Running on oeis4.)