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318- Number Theory Test Two
Definitions, examples, theorems and other things to know on the first number theory test
22
Mathematics
Undergraduate 3
04/12/2010

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Term
Order of an Integer (mod m)
Definition
The least positive integer x that satisfies
a^x== 1 (mod m)

denoted ordm(a)
Term
A Primitive Root (mod m)
Definition
When (a,n)=1 and ordn(a) = phi(n).
*reminder: Phi(n)= # of positive integers
Term
A Quadratic Residue (mod m)
Definition
A solution to x^2 == a (mod m) where (a,m)=1.
Term
A Quadratic Non-Residue (mod m)
Definition
No solutions exist to x^2 == a (mod m) where (a,m)=1.
Term
An Integer Lattice Point
Definition
A point in the plane whose coordinates are integers.
Term
A Convergent
Definition
A "World Champion Approximating Rational Number: that approximates an irrational number. Denoted Cn=Pn/Qn
Term
A Simple Continued Fraction
Definition
A continued fraction expansion whose numerators are all 1's.
Term
An Algebraic Number
Definition
Roots of integral polynomials are algebraic numbers.
Term
The Degree of an Algebraic Number
Definition
The smallest degree of polynomial for which the algebraic number is a root.
Term
Transcendental Number
Definition
A number that is not an algebraic number, meaning it is not a root of an integral polynomial.
Term
Legendre Symbol
Definition
Given a prime p and an integer a, (a,p)=1 then (a/p) = 1 if a is a quadratic residue and (a/p) = -1 if a is a quadratic non-residue.
Term
Prime Number Theorem
Definition
[image]
Term
Tchebychev's Theorem
Definition
For all x>=8,
ln(2)/4 < pi(x)ln(x)/x <30ln(2)
Term
Euler's Criterion
Definition
If p is an odd prime and a is a positive integer satisfying (a,p)=1, then (a/p)==a^((p-1)/2) (mod p)
Term
The Law of Quadratic Reciprocity
Definition
If p and q are distinct odd primes, (p/q)(q/p)=(-1)^(((p-1)/2)((q-1)/2))
Term
Eisenstein's Lemma
Definition
Let p and q be distinct odd primes, and define M and N as follows:
M = [q/p]+[2q/p]+...+[(p-1)/2*q/p]
N = [p/q]+[2p/q]+...+[(q-1)/2*p/q]
Then M+N = ((p-1)/2)((q-1)/2)
Term
Gauss's Lemma
Definition
Let p and q be distinct odd primes and reduce the set {q,2q,3q, ...,(p-1)/2q} of integers modulo p.
If the number of resulting least positive residues larger than (p/2) is m, then (q/p)=(-1)^m
Term
Parity Lemma
Definition
If M = [q/p]+[2q/p]+...+[(p-1)/2*q/p] as in Eisenstein's Lemma, and if m is the least positive residues larger than (p/2), then M and m have the same parity- thatis, they are either both even or odd.
Term
Continued Fraction Algorithm
Definition
Any irrational number X=Xo may be expressed as X=[a0;a1,a2,a3...] where ao=[[Xo]], and if Xn=1/((Xn-1)-[[Xn-1]]), then an=[[Xn]].
Term
Hurwitz's Theorem
Definition
Given any irrational alpha, there exist infinitely many rational numbers p/q, q>0, that satisfy the inequality
|alpha-(p/q)|<1/(sqrt(5)q^2)
Term
Liouville's Theorem, 1844
Definition
If alpha is irrational and algebraic of degree n, there exists a constant c such that for any rational (p/q), q>0, we must have |alpha-(p/q)|>(c/q^n)
Term
Give the "short proof" of the Law of Quadratic Reciprocity
Definition
(p/q)(q/p)=(-1)^m*(-1)^n (by Gauss's Lemma) =(-1)^(m+n) (by rules of exponents)=(-1)^(M+N) (by Parity Lemma)
=(-1)^((p-1)/2)((q-1)/2) (by Eisenstein's Lemma.
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