REPRESENTATIONS OF NATURAL NUMBERS AS SUMS OF NON-NEGATIVE kth POWERS
§ 1. Sums of two squares § 2. The average number of representations as sums of two squares § 3. Sums of two squares of natural numbers § 4. Sums of three squares § 5. Representation by four squares § 6. The sums of the squares of four natural numbers § 7. Sums of m ≥ 5 positive squares § 8. The difference of two squares § 9. Sums of two cubes § 10. The equation $x^3 + y^3 = z^3$ § 11. Sums of three cubes § 12. Sums of four cubes § 13. Equal sums of different cubes § 14. Sums of biquadrates § 15. Waring's theorem