1. 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]

2. a^n \pm 1 for a ≤ 13 and a not a perfect number [http://wwwmaths.anu.edu.au/~brent/factors.html]

3. 2^n \pm 1 for n ≤ 100 [http://www.euronet.nl/users/bota/medium-p.htm]

4. 10^n \pm 1 for n ≤ 100 [http://www.swox.com/gmp/repunit.html]

5. p^p \pm 1 where p is a prime number and p < 180. [http://homes.cerias.purdue.edu/~ssw/bell/r1]

6. 2^{2^n} + 1 (Fermat numbers) [http://www.prothsearch.net/fermat.html]