Hi Robin There is a function factorize() in the package conf.design library(conf.design) factorize(60) [1] 2 2 3 5 Hope this helps Christoph -- Christoph Buser <buser at stat.math.ethz.ch> Seminar fuer Statistik, LEO C11 ETH (Federal Inst. Technology) 8092 Zurich SWITZERLAND phone: x-41-1-632-5414 fax: 632-1228 http://stat.ethz.ch/~buser/