Ask Dr. Math

High School Archive

Browse High School Number Theory
Stars indicate particularly interesting answers or good places to begin browsing.

Selected answers to common questions:
    Diophantine equations.
    Infinite number of primes?
    Testing for primality.
    What is 'mod'?

---

Finding Perfect Cube Factors of 10! [04/12/2005]

To find all perfect cubes that are factors of 10!, you don't need to actually evaluate 10!.

Finding Pi [11/14/1997]

What is the quickest algorithm for finding pi?

Finding Prime Factors of Factorials [11/26/2004]

How many factors of 2 are contained in 100! ?

Finding Prime Numbers [11/10/1997]

What is the fastest way to determine if a number is prime?

Finding Products of a Range of Numbers [03/28/2002]

What method or formula is there to solve for the product of a range of numbers?

Finding Pythagorean Triplets [02/02/2006]

Without using the standard a = n^2 - m^2, b = 2nm, c = n^2 + m^2, how can you work out Pythagorean triplets? For example, how could you find triplets where the hypotenuse exceeds one leg by a certain amount?

Finding Pythagorean Triplets Algebraically [04/13/2002]

Is there a way to find Pythagorean triplets of Type I algebraically?

Finding Sets of 7 Prime Numbers That Sum to 100 [05/22/2007]

There are 35 different sets of 7 prime numbers that sum to 100. Of those sets, which has the largest product, and which has the largest number? I'm using trial and error and it's very frustrating. Is there a better way?

Finding Sets of Integers [01/02/2002]

Without computer assistance, find five different sets of three positive integers such that and k is less than and m is less than n, and 1/k + 1/n + 1/m = 19/84.

Finding the Exponent with a Modulus [05/24/2003]

I am trying to work out k in the following question: 23^k = 201545 (mod 900001).

Finding the Last Digits of a Large Exponential [01/01/2005]

What are the last five digits of 7777777^7777777?

Finding the Sum of the Factors of a Number [07/25/2007]

Is there a formula to find the sum of all the factors of a given number?

Finding the Two Squares [06/11/2003]

One of Fermat's theorems says that every prime number that yields a remainder of 1 when divided by 4 can be expressed as the sum of two integer squares (e.g.: 97 = 4^2 + 9^2). This theorem was proven by Fermat. What methods are known for determining the two squares?

Find Number Given Divisor and Remainder Information [01/21/2009]

A four digit number N leaves remainder 10 when divided by 21, remainder 11 when divided by 23 and remainder 12 when divided by 25. What is the sum of the digits of N?

Find Remainders: 3^2002/26, 5^2002/26 [09/21/2002]

Find the remainders obtained when 3^2002 and 5^2002 are divided by 26; show that 3^2002 + 5^2002 is divisible by 26.

Find the Flaw [08/02/2001]

I don't understand where the following proof goes wrong...

Find the Monster Mod 11, Mod 2310 [05/07/2003]

Find an integer n between 0 and 2309 with the property that 10^10^10^ 34 = n (mod 2310).

Find the Smallest Number... [10/21/1997]

... that has factors of 1, 2, 3, 4, 5, 6, 7, and 8.

Find the Smallest Number - A Remainder Problem [09/27/2001]

Find the smallest number, M, such that: M/10 leaves a remainder of 9; M/9 leaves a remainder of 8; M/8 leaves 7; M/7 leaves 6; M/6 leaves 5; M/5 leaves 4; M/4 leaves 3; M/3 leaves 2; and M/2 leaves 1.

Find the Smallest Triangle [05/25/2001]

A triangle has sides whose lengths are consecutive integers. Its area is a multiple of 20. Find the smallest triangle that satisfies these conditions.

Find the Solution: r^2 + s^2 = c. [01/28/2003]

Given c, find a^2 + b^2 = c^2.

Find the Unknown Base [06/25/2003]

Two numbers are multiplied to equal another number, which generates a false number statement. What base is it?

Finite Series and Greatest Integers [03/06/2003]

For n a positive integer, let t(n) denote the number of positive divisors of n (including n and 1), and let s(n) denote the sum of these divisors. Prove the following:...

Finite vs. Infinite [07/10/1997]

If a line segment is a measurable part of a line, why is the number of points that make up a line segment infinite?

Finite vs. Rational [9/10/1996]

A right triangle with sides 1 and 2 has a hypotenuse equal to the square root of 5, which is irrational - it carries on to infinity without recurring - but the side length of a triangle must be finite!

First Calculation of E [12/18/1997]

How did Euler first calculate the value of e?

The 'First to 100' Game [03/12/2001]

Two players take turns choosing any number from 1-10, keeping a running sum of all the numbers. The first player to make this sum exactly 100 is the winner. Is there a surefire way to win this game?

Fixed Point and Floating Point Numbers [05/19/2000]

What are fixed point or fixed decimal numbers? How do they differ from floating point numbers?

Floating 2 [06/12/2001]

Start with the number 2 on the far left side, then float the number 2 to the far right side; the new number must be three as large as the old number.

Floating-Point Binary Fractions [07/19/1999]

How can you represent fractions such as 12.93 in binary? How do computers represent such numbers?

Floor and Ceiling [05/28/2000]

What do 'floor' and 'ceiling' mean in mathematics?

Forming Palindromic Numbers [12/04/1998]

Can you give me some examples of forming palindromic numbers with different operations? How many steps would it take?

Formula for Connection between Rows of Pascal's Triangle [11/15/2003]

Find a formula connecting any (k+1) coefficients in the nth row of the Pascal Triangle with a single coefficient in the (n+k)th row.

Formula for Counting Triangles [03/16/2000]

How many equilateral triangles of integer-length sides are in an equilateral triangle n units on a side?

Formula for Factors of a Number [11/3/1996]

How many triangles can you draw on a square grid of dots of size x*x?

Formula for Pythagorean Triples [10/23/1997]

Is this formula: a = (m^2-n^2); b = 2mn; c = (m^2+n^2) correct for all Pythagorean triples?

Formula for Sums of Counting Numbers [09/19/2002]

Use the formula for the sum of the first n counting numbers to find 9+ 10+11...+60+61.

Formula for the Extraction of a Digit [06/18/2001]

Is there a formula to extract any digit of a given number?

Formula for the First Day of a Year [03/18/1998]

Is there an equation to find the first day of a year given the year?

Formulas for Primes [09/09/2002]

Prove that n^2 + n + 41 does not always produce a prime number for any whole number n. Explain why n^2 + 8n + 15 never produces a prime number.

Page: [<prev]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 [next>] [last>>]