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Duplicate of A074135.
0

%I #2 Feb 27 2009 03:00:00

%S 1,2,4,3,5,7,6,8,9,13,10,11,12,14,18,15,16,17,19,20,21,22,23,24,25,26

%N Duplicate of A074135.

%K dead

%O 1,2