cp's OEIS Frontend

A342078 Odd digits only come in successive pairs (separated or not by a comma).

%I A342078 #12 Feb 28 2021 10:10:46
%S A342078 1,10,2,3,30,4,5,50,6,7,70,8,9,90,11,20,21,12,22,23,31,13,32,24,25,51,
%T A342078 14,26,27,71,15,52,28,29,91,16,33,40,41,17,72,42,43,34,44,45,53,35,54,
%U A342078 46,47,73,36,48,49,92,55,60,61,18,62,63,37,74,64,65,56,66,67,75,57,76,68
%N A342078 Odd digits only come in successive pairs (separated or not by a comma).
%C A342078 The sequence starts with a(1) = 1 and is always extended with the smallest positive integer not yet present that does not lead to a contradiction.
%e A342078 a(1) = 1 forces the next digit to be a 1 (as odd digits must come in pairs); the smallest positive integer not yet present that starts with a 1 and does not lead to a contradiction is 10. Thus, a(2) = 10;
%e A342078 a(3) = 2 as the smallest positive integer not yet present that does not lead to a contradiction is 2;
%e A342078 a(4) = 3 as the smallest positive integer not yet present that does not lead to a contradiction is 3;
%e A342078 a(5) = 30 as a(5) must start with a 3 (the odd digits must come in pairs) and 30 is the smallest positive integer not yet present that does not lead to a contradiction; etc.
%o A342078 (Python) # see A342076 for aupton, pairsup
%o A342078 mustpair = {1, 3, 5, 7, 9}
%o A342078 print(aupton(67)) # _Michael S. Branicky_, Feb 28 2021
%Y A342078 Cf. A342076, A342077 and A342079 (variations on the same idea).
%K A342078 base,nonn
%O A342078 1,2
%A A342078 _Eric Angelini_, Feb 28 2021