Leonard Euler: Whether ... there are any odd perfect numbers is a most difficult question.
参考文献:
[1]Stan Wagon. The evidence: perfect numbers. Math. Intelligencer, 7(2):66–68, 1985.
[2]Steven Gimbel and John H. Jaroma. Sylvester: ushering in the modern era of research on odd perfect numbers. Integers. Electronic Journal of Combinatorial Number Theory, 3, 2003.
[3]Mathworld. Odd perfect number. accessed, October, 2007.