A276685 - OEIS

%I #8 Sep 14 2016 09:44:21

%S 1,0,2,3,4,6,5,8,20,21,10,22,24,26,29,9,28,7,40,42,30,25,44,32,41,11,

%T 12,23,33,34,45,46,36,48,27,60,50,43,38,61,14,62,64,47,66,52,63,68,16,

%U 80,65,54,67,70,49,82,72,69,84,74,85,55,56,83,86,18,88,200,76,89,90,87,77,78,202,201,100,204,206,92,208,58,220

%N Between two successive odd digits "a" and "b" there are exactly |a-b| even digits.

%C The sequence is started with a(1) = 1 and always extended with the smallest unused integer not leading to a contradiction.

%C The sequence is not a permutation of the natural numbers as 31, for instance, will never appear (according to the definition, 31 should show |3-1| = 2 even digits between " 3 " and " 1 " and doesn't).

%H Jean-Marc Falcoz, <a href="/A276685/b276685.txt">Table of n, a(n) for n = 1..10004</a>

%e Between the first 1 and the first 3 of the sequence, there are indeed |1-3| = 2 even digits (0 and 2).

%e Between the first 3 and the first 5 of the sequence, there are indeed |3-5| = 2 even digits (4 and 6).

%e Between the first 5 and the second 1 of the sequence, there are indeed |5-1| = 4 even digits (8,2,0 and 2).

%e Between the second 1 and the third 1 of the sequence, there are indeed |1-1| = 0 even digits.

%e Between the third 1 and the first 9 of the sequence, there are indeed |1-9| = 8 even digits (0,2,2,2,4,2,6 and 2).

%K nonn,base

%O 1,3

%A _Eric Angelini_ and _Jean-Marc Falcoz_, Sep 13 2016