1,2

The original source for this sequence was the problem 'perlbrac' in the 2009 USACO Holiday Contest (http://ace.delos.com/HOL09) which asked contestants to find the longest sequences of this type that they possibly could. a(n) is the upper bound on the length of such a sequence for a given n.

For example, in the sequence 0, 1, 2, 1, 0, 1, 2 (length 7) consisting of integers in the range [0..2], no two adjacent segments of equal length (e.g. 0, 1, 2 and 1, 0, 1) have the same sum modulo 3. There is also no longer sequence with this property, hence a(3) = 7.

Sequence in context: A117491 A110585 A000412 this_sequence A084631 A002936 A014668

Adjacent sequences: A161807 A161808 A161809 this_sequence A161811 A161812 A161813

hard,more,nonn

Brian Bi (bbi5291(AT)gmail.com), Jun 19 2009

Definition and source corrected by Brian Bi (bbi5291(AT)gmail.com), Sep 19 2009