A277518 - OEIS

%I #13 Aug 31 2021 01:12:29

%S 0,2,1,3,4,5,7,9,10,6,11,13,15,8,17,19,31,33,21,12,35,23,14,37,39,25,

%T 16,51,53,55,27,18,57,59,71,73,29,30,41,75,32,77,43,79,34,91,93,45,95,

%U 36,97,99,110,47,111,49,113,61,115,112,114,117,38,119,131,116,133,135,63,137,118,139,151,130,65,153,132

%N Each even digit k is followed by k odd digits.

%C The sequence starts with a(1) = 0 and is always extended with the smallest integer not yet present that does not lead to a contradiction.

%H Jean-Marc Falcoz, <a href="/A277518/b277518.txt">Table of n, a(n) for n = 1..4160</a>

%e As a(1) = 0, we cannot have for a(2) an integer starting with an odd digit; we then extend the sequence with a(2) = 2; this meads that the next 2 digits must be odd; we thus have a(3) = 1 and a(4) = 3, which are the smallest available integers not yet present in the sequence; a(5) = 4 as a(5) cannot start with an odd digit; this value implies that the next 4 digits must be odd; we thus have a(6) = 5, a(7) = 7, a(8) = 9 and a(9) = 10 -- this integer being the smallest available one that doen't lead to a contradiction; a(10) cannot start with an odd digit as the digit "1" in the previous term "10" is already followed by an even digit ("0"); thus a(10) = 6; etc.

%Y Cf. A277519.

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _Jean-Marc Falcoz_, Oct 19 2016