OFFSET
1,1
COMMENTS
A self-describing sequence. See the sequence as a succession of digits: then a(n) is the position of the even digits of the sequence.
"Lexicographically earliest" refers to comparing sequences term by term, not the strings obtained by the concatenation. (This is not possible, since then the first term could be an arbitrarily long string of 1's.) In other words, term after term, the smallest possible value not leading to a contradiction is appended.
EXAMPLE
We can't have a(1)=1 (since then the first digit would not be even) nor a(1)=2 (since then the first digit would be even), but a(1)=3 is possible.
This implies that there follows another odd digit, a(2)=5, before the first even digit a(a(1))=a(3)=6.
Then comes another odd digit, a(4)=7, since the second even digit occurs only in position a(2)=5, namely a(5)=8.
______________________ 1 _________________ 2 _________________ 3 _ ...
pos. 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 ...
seq. 3,5,6,7,8,2 0,2 1,3 1,3 3,3 5,3 7,3 9,4 0,5 1,5 3,5 5,5 7,5 8,...
The even digits of the sequence are between parentheses here:
Sequence: 3,5,(6),7,(8),(2)(0),(2)1,31,33,35,37,39,(4)(0)...
Positions of even digits: 3, 5, 6, 7, 8, 20, 21... = the sequence itself
CROSSREFS
KEYWORD
base,easy,nonn,nice
AUTHOR
Eric Angelini, Feb 05 2006
EXTENSIONS
Edited by M. F. Hasler, Dec 06 2009
Further edits by N. J. A. Sloane, Dec 19 2009
More terms from Jon E. Schoenfield, May 05 2010
STATUS
approved