Nielsen, Pace P., An upper bound for odd perfect numbers, INTEGERS: the Electronic Journal of Combinatorial Number Theory, 2003, 3: A14 [2013-01-23], (原始内容存档于2017-03-21).
Nielsen, Pace P., An upper bound for odd perfect numbers, INTEGERS: the Electronic Journal of Combinatorial Number Theory, 2003, 3: A14 [2013-01-23], (原始内容存档于2017-03-21).