New result and some open problems on the primitive degree of nonnegative   tensors
  In this paper, we show that the exponent set of nonnegative primitive tensors with order m(\geq 3) and dimension n is {1,2,\ldots, (n-1)^2+1}; and propose some open problems for further research. 
Pingzhi Yuan, Zilong He, Lihua You
math.CO