Periodic sequence 1,2,1,-1,-2,-1...; expansion of (1+x)/(1-x+x^2). 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1
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