cp's OEIS Frontend

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

%I A303785 #9 Dec 01 2019 23:14:36
%S A303785 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 A303785 107,16,109,18,111,20,113,22,115,24,117,26,119,28,121,29,123,30,125,
%U A303785 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 A303785 Lexicographically earliest sequence of distinct terms such that what emerges from the mask is odd (see the Comment section for the mask explanation).
%C A303785 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 A303785 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 A303785 This sequence is a permutation of the integers > 0, as all integers will appear at some point, either as mask or masked.
%H A303785 Jean-Marc Falcoz, <a href="/A303785/b303785.txt">Table of n, a(n) for n = 1..10001</a>
%e A303785 In the pair (1,11), 1 is the mask; 1 emerges and is odd;
%e A303785 In the pair (11,2), 2 is the mask; 1 emerges and is odd;
%e A303785 In the pair (2,13), 2 is the mask; 3 emerges and is odd;
%e A303785 In the pair (13,3), 3 is the mask; 3 emerges and is odd;
%e A303785 ...
%e A303785 In the pair (11019,2018), 2018 is the mask; 9 emerges and is odd;
%e A303785 etc.
%Y A303785 Cf. A303782 (same idea with primes), A303783 (with squares), A303784 (with even numbers), A303786 (rebuilds the sequence itself term by term).
%K A303785 nonn,base
%O A303785 1,2
%A A303785 _Eric Angelini_ and _Jean-Marc Falcoz_, Apr 30 2018