See also the
Dr. Math FAQ:
3D and higher
Browse Middle School Prime Numbers
Stars indicate particularly interesting answers or
good places to begin browsing.
Selected answers to common questions:
Testing for primality.
- Prime Numbers [01/31/1997]
What are the prime numbers and why are they prime numbers?
- Prime Numbers vs. Prime Factors [01/13/1997]
What is the difference between a prime number and a prime factor?
- 1 and 0: Prime or Composite? [10/06/1997]
Is the number one a prime or a composite number? Why? What about zero?
- 400-Digit Product of Two Primes [11/04/2002]
What two prime numbers when multiplied together will equal a 400-digit
- Abundant and Deficient Numbers [10/14/1997]
What are abundant and deficient numbers, and what are they used for?
- Adjacent Primes [11/26/2001]
What are adjacent primes?
- Checking if a Number from 1-100 is Prime [09/06/2008]
Is there an easy way to determine if a number between 1 and 100 is
prime without having to do a lot of division?
- Classifying the Number One [11/27/1998]
My students have learned about prime and composite numbers. What
classification fits the number 1?
- Code with Only a String of 1's [10/28/2002]
You need to send a numeric code to someone, such as one used to
unlock a padlock.
- Determining if a Large Number is Prime [05/05/2004]
Is 333667 a prime? I have ruled out all evens plus 5, 10, 7, 8, 9,
13, 17, and 19 as possible factors but do not know how to proceed from
- Determining If a Number is Prime [08/12/2004]
Is there a formula for determining if a number is prime?
- Etymology of the Word Prime [08/28/2002]
Why are prime numbers called prime?
- Euclid's Algorithm for Finding a GCD [10/12/2002]
Find the only number besides one that is a common factor of 163231,
152057, and 135749.
- Factoring Very Large Numbers into Primes [12/05/2003]
Is there a way to factor really big numbers into primes other than the
usual method of dividing by successive primes?
- Factors and Multiples [01/27/1998]
My son is in 4th grade and needs help naming a common multiple of a pair
- Factors and Primes [09/10/1997]
A prime number is a number greater than 1 and has only 2 divisors, 1 and
itself. Without the stipulation greater than one, what would be the
- Fastest Primality Test? [12/21/2005]
I found an article on the Internet discussing a new test to determine
if a given number is prime or composite. Is it the fastest test?
- Finding Prime Factors of Factorials [11/26/2004]
How many factors of 2 are contained in 100! ?
- Finding Prime Numbers [12/5/1995]
What is the easiest way to find a prime number?
- General Formula to Find Prime Numbers? [10/12/2005]
I was wondering if it is possible that there exists a general formula to know what numbers are prime, or has it been proven that no such formula could exist? What evidence do we have for either case?
- How does the Sieve of Eratosthenes Work? [10/29/2002]
How does the Sieve of Eratosthenes work for finding prime numbers?
- How Many Primes Are Known? [01/21/2003]
How many prime numbers are currently known?
- The Importance of 1 Not Being a Prime Number [04/25/2009]
Does division by zero make sense in a field of cardinality 1? If there
is only one element, the multiplicative and additive identities must
be the same, so 0 = 1 and 1/0 = 1/1 = 1. Is that true?
- Infinite Primes [12/4/1994]
We would appreciate it if you could send us the largest prime to date,
and how many digits it has.
- Is Zero Prime or Composite? [10/23/1995]
Is zero prime, composite, or neither?
- Largest Prime Number [9/8/1996]
What is the largest prime number yet found?
- Least Common Multiple, 2-10 [10/28/2002]
Find the smallest counting number that is divisible by the numbers 2
- No Largest Prime Number [8/19/1996]
What's the largest prime number? (proof by contradiction).
- Numbers with Large Exponents [08/22/2001]
How many zeros end the number 2^300 * 5^600 * 4^400?
- Perfect Numbers [08/14/1997]
What is the highest perfect number that has been found? How many perfect
numbers are there? What are they?
- Perfect Numbers - Basics, History [11/3/1996]
What is the next perfect number after 28?
- Prime and Composite Numbers, Sieve of Eratosthenes [01/28/1997]
I need a list of all prime numbers and all composite numbers up to 50.
- Prime and Consecutive Numbers [11/16/2001]
Why are 3, 5, and 7 the only numbers that appear to be prime and
- Prime, Composite, or Neither? [09/16/2003]
What are prime and composite numbers?
- Prime Factors [01/28/2006]
What is a number with only two prime factors and no repeated factors?
- Prime Number 2001, Sieve of Eratosthenes [01/25/1997]
Is 2001 a prime number?
- Prime Numbers: 20-30 [01/31/1997]
What are the prime numbers 20 through 30?
- Prime Numbers and the Sieve of Eratosthenes [10/20/2003]
How can I figure out the last or largest prime number I need to use in
the 'Sieve of Eratosthenes' in order to find all the primes between 1
- Prime Numbers in Cryptography [08/14/1999]
What are some practical uses of prime numbers?
- Prime Number Tests [11/12/1998]
Is the number 55409243 prime? How can you test to see whether a number is