Proof of a Conjecture of Helleseth: Maximal Linear Recursive Sequences   of Period $2^{2^n}-1$ Never Have Three-Valued Cross-Correlation
  We prove a conjecture of Helleseth that claims that for any $n \geq 0$, a pair of binary maximal linear sequences of period $2^{2^n}-1$ can not have a three-valued cross-correlation function. 
Daniel J. Katz
math.CO cs.IT math.IT