10.12.2012 Views

Prime Numbers

Prime Numbers

Prime Numbers

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

114 Chapter 2 NUMBER-THEORETICAL TOOLS<br />

Establish the corollary that the number of pairs of consecutive quadratic<br />

residuesis(p − 5)/4, (p − 3)/4, respectively, as p ≡ 1, 3 (mod 4). Using the<br />

formula for N(a, b), prove that for every prime p the congruence<br />

x 2 + y 2 ≡−1(modp)<br />

is solvable.<br />

One satisfying aspect of the N(a, b) formula is the statistical notion that<br />

sure enough, if the Legendre symbol is thought of as generated by a “random<br />

coin flip,” there ought to be about p/4 occurrences of a given pair (±1, ±1).<br />

All of this makes sense: The Legendre symbol is in some sense random.<br />

But in another sense, it is not quite so random. Let us estimate a sum:<br />

sA,B = <br />

<br />

x<br />

,<br />

p<br />

A≤x

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!