Tor Helleseth Alexander Kholosha m-Sequences of Lengths 2<sup>2k</sup>-1 and 2<sup>k</sup>-1 with at Most Four-Valued Cross Correlation. 106-120 2008 SETA http://dx.doi.org/10.1007/978-3-540-85912-3_10 conf/seta/2008 db/conf/seta/seta2008.html#HellesethK08