Puzzles sites

1.- Frank Rubin Contest Center
2.-  Macalester College POTW
3. Ed Pegg, Jr. MathPuzzle pages.
4.- Claudio Meller's "Simplemente Números"

Number patterns

1.- Patrick De Geest, World of Numbers  
2.- Magic Stars and other patterns by Harvey Heinz
3. Shyam Sunder Gupta's Number recreations

4. Mutsumi Suzuki, Magic Squares. Here is my pdf version of the Mr. Suzuki's pages.


General references

1.- The Chris Caldwell Site
2.- Wolfram MathWorld
3. The On-Line Encyclopedia of Integer Sequences® (OEIS®), founded by Neil J. A. Sloane in 1964.
4.- Prime Curios!, by G. L. Honaker, Jr. & Chris Caldwell
5.- Mudd Math Fun Facts, by Francis Edward Su.
6. by T. D. Noe.
7. Some pages about prime-records

Codes for primes

1.- Proth.exe, by Yves Gallot. For the GFN search click here
2.- Fermat.exe for hunting small Fermat's prime factors, by Leonid Durman.
3. Mersenne primes search by GIMPS.
4. Ubasic V 8.74 & several versions here including the Malm collection of sample programs.
5. Zzmath.xll is an add-in, created by Joe Crump for Excel worksheets, that provides 30 useful  number theory functions.

On Line applets

1. Factorization:
a) Jack Brennen.
b) Factoris, by XIAO Gang.
c) ECM by Dario Alpern.

2. Primality:
a) The Nth prime page
b) Germany
c) Primes by XIAO Gang.
d) Caltech

3. The number Empire (Factorization, Primality & others) by Vitalii Vanovschi.

4. Numbers Aplenty (interesting natural numbers and their properties) by Giovanni Resta.

5. Count, Sum, Reversing digits and Digital root of an integer (all this in the same box!)

6. Remove spaces

7. Palindromeness checkers A, B.

8. Numbers base converter.

9. Numbers and currencies to words converter. It supports 20 languages

FAQ pages

1.- This site FAQ Page
2.- Chris Caldwell's Frequently Asked Questions about Primes
3.- Ask Dr Math's FAQ Page about many mathematic issue.
4. Looking for lost web pages? Use this link.