       Numbers everywhere, some lead, some follow SHOW ALL BY ALPHABET SHOW ALL BY CATEGORIES UNITS OF MEASURE MATH AND CALCULATORS ANYTHING FOR FUN GAMETOOLS ABOUT US       Prime Numbers Please enter a number: A number p is prime if it is a positive integer greater than 1 and is divisible by no other positive integers other than 1 and itself.  Thus the first few prime numbers are 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, ... Positive integers greater than 1 that aren't prime are called composite integers. NoteThere is a limit to how big of a number you can check, depending on your browser, and operating system. When calculating prime numbers larger than 99999999999999 be sure to check if the calculator changed your number.

Prime numbers are used in cryptography. The RSA cryptography system consists of two large prime numbers chosen by the user. The enciphering key is the product of these two primes. Because it is extremely difficult and time consuming to factor large numbers, it is practically impossible to find the deciphering key.

Banks also use prime numbers to provide security for ATM machines, etc.

The Prime Machine [JAVA] at the University of Utah The applet on this page lets you explore the set of prime numbers.  