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(原始内容存档于2013-12-31). R.G.E. Pinch (1998), Economical Numbers. Chris Caldwell, The Prime Glossary: extravagant number (页面存档备份,存于互联网档案馆) at The PrimePages.
The Top Twenty: Primorial (页面存档备份,存于互联网档案馆) at The PrimePages(英语:PrimePages). 埃里克·韦斯坦因. Primorial Prime. MathWorld. Harvey Dubner, "Factorial and Primorial