John J O'Connor; Edmund F Robertson. The number e. School of Mathematics and Statistics. University of St Andrews, Scotland. [2011-06-13]. (原始内容存档于2015-09-08).
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John J O'Connor; Edmund F Robertson. The number e. School of Mathematics and Statistics. University of St Andrews, Scotland. [2011-06-13]. (原始内容存档于2015-09-08).