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This sequence O (made exclusively of odd numbers) becomes the sequence E (made exclusively of even numbers) by switching everywhere in O the two digits that are in contact with a comma. No repeated terms are allowed in O or E and we want O to be the lexicographically first such sequence.
1

%I #9 Mar 11 2016 21:29:57

%S 1,21,23,41,25,61,27,81,29,201,203,43,45,63,47,83,49,205,401,65,67,85,

%T 69,207,601,87,89,209,801,211,213,403,405,603,407,803,409,215,411,605,

%U 607,805,609,217,611,807,809,219,811,221,223,413,415,613,417,813

%N This sequence O (made exclusively of odd numbers) becomes the sequence E (made exclusively of even numbers) by switching everywhere in O the two digits that are in contact with a comma. No repeated terms are allowed in O or E and we want O to be the lexicographically first such sequence.

%C Here are the first terms of O and E, compared:

%C O = 1,21,23,41,25,61,27,81,201,203,43,45,63,47,83,401,205,...

%C E = 2,12,14,32,16,52,18,72,102,104,34,36,54,38,74,302,106,...

%H Cf. A270119.

%K nonn,base

%O 1,2

%A _Eric Angelini_ and _Lars Blomberg_, Mar 11 2016