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Deletions are marked like this.  Additions are marked like this. 
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* $b^n \pm 1$ for $b = 2, 3, 5, 6, 7, 10, 11, 12$ and large exponents n [http://homes.cerias.purdue.edu/~ssw/cun/index.html]  * $a^n \pm 1$ for $a = 2, 3, 5, 6, 7, 10, 11, 12$ and large exponents n [http://homes.cerias.purdue.edu/~ssw/cun/index.html] 
a^n \pm 1 for a = 2, 3, 5, 6, 7, 10, 11, 12 and large exponents n [http://homes.cerias.purdue.edu/~ssw/cun/index.html]
a^n \pm 1 for a ≤ 13 and a not a perfect number [http://wwwmaths.anu.edu.au/~brent/factors.html]