Next: About this document ...
Up: Lecture 21: Binary Quadratic
Previous: Computing and
Every natural number is a sum of four squares. See pages
124-126 of Davenport for a proof.
A natural number is a sum of three squares if and only if it is not a
power of times a number that is congruent to modulo . For
example, is not a sum of three squares. This is more difficult to
prove.
William A Stein
2001-10-31