@article{10_4064_aa109_4_7,
     author = {Florian Luca and Igor E. Shparlinski},
     title = {Average multiplicative orders of elements modulo $n$},
     journal = {Acta Arithmetica},
     pages = {387--411},
     publisher = {mathdoc},
     volume = {109},
     number = {4},
     year = {2003},
     doi = {10.4064/aa109-4-7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa109-4-7/}
}