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 ≤ 13 and a not a perfect number [http://wwwmaths.anu.edu.au/~brent/factors.html]
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 ≤ 13 and a not a perfect number [http://wwwmaths.anu.edu.au/~brent/factors.html]