Date: Fri, 1 Jul 2005 11:56:38 +0000
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1 3 2 6 7 5 4 12 13 15 14 10 11 9 8 24 25 27 26 ?

1 3 2 6 7 5 4 12 13 15 14 10 11 9 8 24 25 27 26 ...
Positive integers in binary, for each 1 bit (not changed) flip the next bit.
This can also be phrased in reversing sequences of numbers.
More simply, just the integers in reflective-Gray-code order.