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Browse College Number Theory
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Testing for primality.
 Congruence Class of 10^n Modulo 11 [04/14/2003]

What is the congruence class of 10^n modulo 11? Use this to determine
the remainder when 654321 is divided by 11.
 Conjectures vs. Hypotheses [01/12/1999]

What is the difference between the terms 'conjecture' and 'hypothesis'?
Should the Riemann hypothesis be the Riemann conjecture?
 Consecutive Composite Numbers [07/05/2002]

Find 1000 consecutive composite numbers.
 Consecutive Composite Numbers [06/07/2005]

Is it possible to find m consecutive composite numbers where m is any
natural number?
 Consecutive Integer Proof [09/16/2004]

Is it possible to prove that the product of five consecutive integers
cannot be a perfect square?
 Counting Infinities [04/29/1997]

I think I have found a flaw in the uncountability proof. Is this
possible?
 Counting Unique Rational Numbers [11/16/2008]

How many unique simple forms of rational numbers are there of the form
p/q, where p and q are nonzero whole numbers less than or equal to n?
For example, 1/2 and 2/4 have the same simple form, so they are not
considered unique. The answer should be a function of n.
 Cubes as Differences of Squares [07/04/2002]

Prove that the cube of any positive integer is equal to the
difference of the squares of two integers.
 Cubic Diophantine Equation in Three Variables [09/10/2004]

Find integer solutions of the equation x^3 + y^3 = 31z^3. I know the
fundamental solution is (137, 65, 42), but I want to have all the
values positive. I know also that there is an arithmetic procedure
(doubling in the group) to obtain further solutions from the
fundamental one, but I do not know the details of this procedure.
 Cyclic Redundancy Check [06/26/2002]

I understand how cyclic redundancy checks work, but I fail to see how
appending zeros to the message string (before the division) provides an
advantage.
 Decomposition of Primes as the Sum of Two Squares [12/17/2005]

If you write a prime number p as a sum of two squares, can you prove
that its decomposition a^2 + b^2 is unique for (a,b up to +/ 1)?
 Degree of Error in pi(x) Approximation [10/20/2004]

How does the error in the formula x/ln(x), used to approximate pi(x)
(the primes counting function), behave for large values of x?
 Determine b if (a+b)/5 = (b1)/2 [07/25/2003]

Both a and b are 4 fourdigit numbers, a is greater than b, and one
number is obtained from the other by reversing the digits. Determine b
if (a+b)/5 = (b1)/2.
 Difference of Square Numbers [07/18/2008]

Can one number ever be represented as two distinct differences of
squares? Or is every difference of square numbers unique?
 A Diophantine Determined with a DataDriven Approach [06/24/2012]

A student wonders if a usubstitution would solve a troublesome Diophantine
equation. Doctor Vogler takes up the struggle with a false start of his own, before
noticing helpful patterns from a computational attack and walking the student through
the thought process behind his strategy.
 Diophantine Equation [08/25/2007]

Find all integer solutions (a,b) such that (1abab)/(1ab+a+b) is an
integer.
 Diophantine Equations in Three Variables [10/30/2004]

I need to know how to get positive integer solutions of two
Diophantine equations having three variables. For example: 2x + 3y +
7z = 32 ; 3x + 4y  z = 19. (Give the positive set of triples for the
above equations.)
 Diophantine Equation Solved by Reasoning [04/05/2006]

Find all integer solutions of (1/m) + (1/n)  (1/mn^2) = 3/4.
 Diophantine Equations, Step by Step [10/01/2002]

Find all positive integer solutions to 43x + 7y + 17z = 400.
 Diophantine Equation with Three Unknowns [09/28/2009]

Find all triples of positive integers (x,y,z) such that xyz + xy + yz
+ zx + x + y + z = 243.
 Diophantine Equation with Three Variables [02/01/2006]

Find all positive integer solutions (a,b,c) that satisfy the equation
a + b + c + ab + bc + ca = abc + 1.
 Diophantine System of Equations [12/31/2004]

I'm trying to find the rational solutions (in parametric form) to the
set of two simultaneous equations:
x^2 + x = y^2
x^2 + 1 = z^2
 Direct Conversion of Binary to Octal [05/14/2002]

How can you convert from base 2 to base 8 without going through base
10?
 Discrete Logarithm Problem [10/13/2004]

Given a === b^c mod N. When a, b, and N are given, can we find c?
 Distances between Rational and Irrational Numbers [01/13/2005]

Is it true that if x  p/q < x  r/s with x irrational and p/q,
r/s irreducible rationals then q > s? If so, how can you prove it?
 Divisibility by 8 [04/14/1997]

Show that, if n is a positive integer, then 5^n+2*3^(n1) + 1 is
divisible by 8.
 Divisibility Proof [02/16/2001]

How can I prove that if n is an odd positive integer, then 2269^n +
1779^n + 1730^n  1776^n is an integer multiple of 2001?
 Divisibility Proof by Cases [02/23/2003]

Prove that if dn, then (2^d  1)(2^n  1).
 Do Rational and Irrational Numbers Alternate? [10/13/2000]

If any two nonequal real numbers "contain" an irrational, and any two
nonequal real numbers "contain" a rational, do rational and irrational
numbers alternate?
 Elliptic Curve Factorization [02/10/2006]

I would like to find out how to develop the parameters of a cubic
parabola in general so that I can implement an integer factorization
method. I would also like to know how to add points such as P+P and
P+Q to such a curve.
 Elliptic Curve Resources [05/04/2007]

Is there an algorithm to determine the rank of a general elliptic
curve? What are some good books to start learning about elliptic curves?
 Equation with Two Exponential Terms [06/27/2009]

Find all ordered pairs (a,b) for which 3^a + 7^b is a perfect square.
 Erdos' Proof [04/03/1997]

Can you show me Erdos' proof that there is a prime number between every
integer n and 2n?
 Euclidean Algorithm [5/13/1996]

How can we prove that Euclid's method for finding the highest common
factor for two numbers will work for all values?
 Euclidean Algorithm and Linear Equations [11/03/2003]

Could you please explain step by step how to use the Euclidean
Algorithm to solve a linear equation and find x and y integers?
 Euclidean Algorithms [3/13/1996]

What is the Euclidean algorithm? What is a "constructible" number? What
can you tell me about Diophantine equations?
 Euclidean and Division Algorithms [11/26/1997]

Can you show and explain the proofs of the Euclidean Algorithm and the
Division Algorithm?
 Euclid's Extended Algorithm [09/16/2001]

Can you please state for me the steps of Euclid's extended algorithm in
simple terms?
 Euler's Phi Function Applied to Large Numbers [08/23/2004]

I'm trying to find the phi value of a large (10digit) composite
number. Can it be done in polynomial time, and if so, is there an
algorithm?
 Expansion of n(n+1)(n+2)...(n+k) [07/15/2002]

Is the expansion of n(n+1)(n+2)...(n+k) known?
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