1. Protheroe, N.: What does good math instruction look like? Principal 7(1), 51–54 (2007)
2. Rademacher, H., Toeplitz, O.: The Enjoyment of Math. Princeton University Press, Princeton (1957)
3. Obreshkov, N.: Number Theory. University Publishing House, St. Kl Ohridski (2004). (in Bulgarian)
4. Crandall, R., Pomerance, C.: Prime Numbers. A computational perspective Springer-Verlag, New York (2001)
5. Rosen, K.: Elementary Number Theory and lts Applications. Addison-Wesley Publishing Company, Boston (1986)