cp's OEIS Frontend

A303849 Lexicographically earliest sequence of distinct terms such that what emerges from the mask (right-aligned) is even (see the Comments section for the mask explanation).

%I A303849 #9 Jun 24 2018 13:28:44
%S A303849 1,20,2,21,3,22,4,23,5,24,6,25,7,26,8,27,9,28,200,10,201,11,202,12,
%T A303849 203,13,204,14,205,15,206,16,207,17,208,18,209,19,210,29,211,30,212,
%U A303849 31,213,32,214,33,215,34,216,35,217,36,218,37,219,38,220,39,221,40,222,41,223,42,224,43,225,44,226,45,227,46,228,47
%N A303849 Lexicographically earliest sequence of distinct terms such that what emerges from the mask (right-aligned) is even (see the Comments section for the mask explanation).
%C A303849 For any pair of consecutive 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 right. What is not covered by the mask forms an even number on the left.
%C A303849 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 A303849 This sequence is a permutation of the positive integers, as all integers will appear at some point, either as mask or masked.
%C A303849 Comparing the two b-files (the first 10000 terms), this seems to be a duplicate of A303847. - _R. J. Mathar_, Jun 23 2018
%H A303849 Jean-Marc Falcoz, <a href="/A303849/b303849.txt">Table of n, a(n) for n = 1..10001</a>
%e A303849 In the pair (1,20), 1 is the mask; 2 emerges and is even;
%e A303849 in the pair (20,2), 2 is the mask; 2 emerges and is even;
%e A303849 in the pair (2,21), 2 is the mask; 2 emerges and is even;
%e A303849 in the pair (21,3), 3 is the mask; 2 emerges and is even;
%e A303849 ...
%e A303849 in the pair (117,2018), 117 is the mask; 2 emerges and is even;
%e A303849 etc.
%Y A303849 Cf. A303784 (same idea, but the mask is left-aligned).
%K A303849 nonn,base
%O A303849 1,2
%A A303849 _Eric Angelini_ and _Jean-Marc Falcoz_, May 01 2018