* 
Asterisk indicates free registration is required for this
website, e.g. Project Euler 


Nick's Mathematical Puzzles
 more than one hundred excellent puzzles of varying degrees of
difficulty, each with hints, an answer, and a complete solution. 


Ponder
This is one math or logic puzzle a month. All readers may send
in solutions. Solvers are honored by having their names appear on
the puzzle page. Past problems and solutions are archived on the
website, going back to May 1998, so by April, 2007 there were nine full
years  108 challenges  archived for your enjoyment. 


Project Euler * is
a collection of challenging mathematical/computer programming problems
that will require mathematical insights and computer programming skills to
solve. The website keeps track of problems you have solved, and can
show you problems you haven't solved yet. See also forum.projecteuler.net
* 

Purdue University
Problem of the Week 
A Purdue Math Department panel publishes a challenging problem once a week and invites college & precollege students, faculty, and staff to submit solutions. Our objective is to stimulate and cultivate interest in good mathematics, especially among younger students. 

The Problem Site 
Here you will find math problems, word games, word puzzles, mystery quests, and many other free educational resources. 


Nrich
Ask
Nrich *

The University of Cambridge. For problems click
"This Month" or the categories under it  Stage 4 & 5 are
the hardest problems. Also, look for the Tough Nuts link. For
previous problems, choose a year and month under Past Issues.



Puzzleup is a weekly
puzzle competition. 


Alma
College Hich School Math Challenge  A new problem each month for
students at participating high schools. Students may submit their
solutions. The best solution will be published (giving credit to the
solver, and earning the solver an Alma College tshirt) and a list of all
students who submit correct solutions will be published as well. 

Problem
of the Week

Collegelevel
problems, posted weekly for the
current semester by Professor Alberto L. Delgado, with archives of
problems and solutions starting in spring 1997, for number theory,
combinatorics, probability, calculus, etc. 

ken.duisenberg.com/potw 
A weekly puzzle for advanced high school or college level,
with a math, geometry, or game focus. The problems are easy to understand
but tricky to solve. An archive of previous problems and solutions is
included, together with a list of other puzzle sites Ken has enjoyed
visiting. 


A site devoted to original mathematical recreations. If you
have a math puzzle, discovery, or observation, you are invited to email
the author. You can also submit answers to the problem of the month;
questions and solutions are archived. Examples include: Divisor Chains;
Integer Square Tilings; Angle Frequencies; Disconnected Polyominoes;
Average Arrays; Convex Spectra; Surround Numbers; Palindrome Products,
Fairy Chess Endgames, and Rectangles in Squares. 

Problem
Corner 
 Les Reid; Southwest Missouri State University (SMSU).
High School, Advanced, and Challenge problems, updated monthly, plus links
to other problem sites. At the advanced and challenge levels,
solutions are solicited and the names of those solving the puzzle are
posted monthly along with one solution. 

Maths problems
"Kalva currently includes about 4,100 olympiad problems and about
1,700 other problems. I have given solutions for about 2,300
Olympiad problems (and almost all the Putnam and AIME problems). My
ultimate objective is to include a wide variety of interesting problems of
all levels of difficulty. In general, I have no interest in pure bookwork
problems." 
Preolympiad problems

International/Regional Olympiad problems

Undergraduate problems

Miscellaneous problems

AIME,
Dudeney 
IMO,
IMO shortlist,
APMO, AustrianPolish,
Balkan, Junior
Balkan, Centroamerican,
Iberoamerican 
Putnam,
Newman, IMC,
Vietnam 
Misc 

National Olympiads

Suggested books



ASU,
Brasil, Canada,
Indian, Irish,
Kürschák/Eötvös,
Mexico, Polish,
Russian,
Spanish, Swedish,
USA, Vietnam 
Elementary
books 







U.S. Military Academy Problem
of the Week
A current collegelevel Problem of the Week, with links to past
problems and solutions, a project of the Pi Mu Episilon chapter of the
United States Military Academy. MathCad or Word are needed to view
past problems and solutions. 

MathPuzzle.com is an absolutely ginormous
compendium of puzzles of all kinds (math, logic, word, mechanical 
you name it) along with a huge number of links
to websites with background information and more puzzles. 



An eclectic mix of popular puzzles, short films, the shakespeare puzzle, articles, biography, books, guestmap, fun page, forum, and links.
This is a great site to explore. Go to the "fun page" and
look for links to a version of the Lunar Lander game, for example.
(Barry's old site was homepage.ntlworld.com/barry.r.clarke) 


The Harbour
Puzzle  Oskar's Harbour Puzzle: M. Oskar van Deventer
5 January 2002 (Original design: 16111989). Object: Move all
containers plus cranes from the quay onto the ship.
Rule 1: A crane can only move itself and things below it (including other
cranes)
Rule 2: For stability, there can never be empty space below a crane. 


pqrst
means puzzles, quarterly, rate, solve, ten. The idea was that every
quarter there would be ten puzzles that people would rate as to how
enjoyable they are, and they would solve. It's been a few years
since there were any new puzzles on this site, but the archives are
extensive. 


Aha!
Puzzles are 168 very clever puzzles, each with its own very welldone
graphic. To find them, click the "puzzles" link, then
click the links at the bottom of each page to advance through the puzzles. There are answers to all but the last three, as of
1/20/2008. 


Math Test Links
This section has sample test papers from math tests that are used to
challenge (and in some cases, select) the brightest high school students.


STEP Mathematics: a resource for teachers and students;
Supermaths: Mathematics' workshops for young students in Newcastle upon Tyne, UK;
Examinations' solutions' Library: for GCSE Mathematics (MEI) and GCE A/ASlevel Structured Mathematics (MEI).
A proof of pi's irrationality;
A proof of e's irrationality;
Meikleriggs' homepages;
Other links 



OCR  Oxford, Cambridge, and RSA
Examinations 




Riddles and other nonmathematical puzzle sites
 samuelloyd.com — click the sam lloyd's puzzles link on the main page.
 www.dansmath.com/probofwk/probofwk.html —
suitable for grade school kids.
 colstate.edu/mathcontest/
Columbus State University Math Contest, suitable for grade school kids; a
new problem every Monday
Puzzle Links
 The Math Forum @ Drexel lists
hundreds of sites that have math puzzles. Also, though the Drexel POW
site requires a "library card", it lists a
good number of other problem sites by the level of math
required.
Old sites that, alas, no longer exist:
 www.shepherd.edu/mathweb/problems.html still
exists, but it is no longer updated with new problems.
 www.olemiss.edu/mathed/pow is
no longer updated, but has an archive of puzzles that will be fun for
elementary school children. This site moved to www.umassd.edu/mathcontest,
and then will move again to Columbus State University in Georgia.

MARP
 Mark's Archive of Riddles and Puzzles, by Michael Winckler
