On the linear complexity of binary threshold sequences derived from Fermat quotients

We determine the linear complexity of a family of p ²-periodic binary threshold sequences derived from Fermat quotients modulo an odd prime p, where p satisfies ${2^{p-1} \not\equiv 1 ({\rm mod}\, {p^2})}$ . The linear complexity equals p ² ? p or p ² ? 1, depending whether ${p \equiv 1}$ or 3 (mod 4). Our research extends the results from previous work on the linear complexity of the corresponding binary threshold sequences when 2 is a primitive root modulo p ². Moreover, we present a partial result on their linear complexities for primes p with ${2^{p-1} \equiv 1 ({\rm mod} \,{p^2})}$ . However such so called Wieferich primes are very rare.