Roberto Maria Avanzi Gerhard Frey Tanja Lange Roger Oyono On using expansions to the base of -2. 403-406 2004 81 Int. J. Comput. Math. 4 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=0020-7160&volume=81&issue=4&spage=403 db/journals/ijcm/ijcm81.html#AvanziFLO04