Prime and Composite Numbers

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Questions and Answers

Which of the following best describes the relationship between a composite number and its factors?

  • A composite number is always an odd number.
  • A composite number can be expressed as a product of two smaller natural numbers. (correct)
  • A composite number has no factors other than itself.
  • A composite number is only divisible by 1 and itself.

Why are prime numbers considered central in number theory?

  • They can be used to generate all composite numbers.
  • Every natural number greater than 1 can be expressed as a unique product of primes. (correct)
  • They are the most frequently occurring numbers.
  • They form the basis for encryption algorithms.

What does it mean for a number to be 'factorized'?

  • It has been expressed as a product of prime numbers. (correct)
  • It has been expressed as a sum of prime numbers.
  • It has been determined to be a prime number.
  • It has been divided to its smallest possible value.

Which primality test is faster, but has a small chance of error?

<p>Miller-Rabin primality test (A)</p> Signup and view all the answers

What is a key difference between the Miller-Rabin primality test and the AKS primality test?

<p>The Miller-Rabin test is faster but has a chance of error, while the AKS test is slower but always correct. (D)</p> Signup and view all the answers

What is the primary limitation of using the AKS primality test in practical applications?

<p>It is too slow for large numbers. (B)</p> Signup and view all the answers

What makes Mersenne numbers particularly interesting in the context of prime numbers?

<p>Particularly fast methods are available to test if they are prime. (D)</p> Signup and view all the answers

As of October 2024, what is known about the largest discovered prime number?

<p>It is a Mersenne prime. (B)</p> Signup and view all the answers

What significant contribution did Euclid make to the study of prime numbers?

<p>He proved that there are infinitely many primes. (A)</p> Signup and view all the answers

What does the Prime Number Theorem describe?

<p>The probability of a randomly chosen large number being prime. (D)</p> Signup and view all the answers

According to the prime number theorem, what is the relationship between the number of digits in a large number and the probability of that number being prime?

<p>Inversely proportional (D)</p> Signup and view all the answers

What does Goldbach's conjecture propose regarding even integers greater than 2?

<p>They can all be expressed as the sum of two primes. (C)</p> Signup and view all the answers

What defines 'twin primes' according to the twin prime conjecture?

<p>Two primes that differ by 2. (B)</p> Signup and view all the answers

What two branches of number theory have been spurred by questions regarding prime numbers?

<p>Analytic and algebraic (D)</p> Signup and view all the answers

What is 'primality'?

<p>The property of being a prime number (B)</p> Signup and view all the answers

Which method for checking primality involves testing whether a number is a multiple of any integer between 2 and its square root?

<p>Trial division (D)</p> Signup and view all the answers

Which statement accurately describes the factorization of natural numbers greater than 1?

<p>They are either prime or can be factorized as a product of primes unique up to their order. (A)</p> Signup and view all the answers

If a large number is randomly chosen, what mathematical function is its probability of being prime inversely proportional to?

<p>Logarithm (B)</p> Signup and view all the answers

Which of the following is a characteristic of a prime number?

<p>It is a natural number greater than 1. (B)</p> Signup and view all the answers

Which task does 'trial division' accomplish in the context of number theory?

<p>Checking if a number is prime (B)</p> Signup and view all the answers

Flashcards

Prime Number

A natural number greater than 1 that is not a product of two smaller natural numbers.

Composite Number

A natural number greater than 1 that is not prime; it can be written as a product of smaller numbers.

Fundamental Theorem of Arithmetic

Every natural number greater than 1 is either a prime number or can be uniquely factored into a product of primes.

Primality

The property of a number being prime.

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Trial Division

A simple primality test that checks if a number is divisible by any integer between 2 and the number itself.

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Miller-Rabin Primality Test

A primality test that is fast but has a small chance of error.

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AKS primality test

A primality test that always produces the correct answer in polynomial time but is too slow to be practical.

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Mersenne numbers

Prime numbers of the form 2^n - 1.

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Infinitude of Primes

There are infinitely many primes.

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Prime Number Theorem

A theorem stating that the probability of a randomly chosen large number being prime is inversely proportional to its number of digits.

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Goldbach's conjecture

Every even integer greater than 2 can be expressed as the sum of two primes. (Unproven)

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Twin Prime Conjecture

There are infinitely many pairs of primes that differ by two.

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Study Notes

  • A prime number is a natural number greater than 1, and it can't be expressed as a product of two smaller natural numbers.
  • A composite number is a natural number greater than 1 that is not prime.
  • The number 5 is prime since its only products (1 × 5 or 5 × 1) involve 5 itself.
  • The number 4 is composite because it can be expressed as a product (2 × 2), where both numbers are smaller than 4.
  • Primes are central to number theory due to the fundamental theorem of arithmetic.
  • The fundamental theorem of arithmetic states that every natural number greater than 1 is either prime or can be factorized into a unique product of primes.
  • The property of being prime is called primality.

Determining Primality

  • One method, trial division, involves whether a number is a multiple of any integer between 2 and itself.
  • The Miller-Rabin primality test is faster, but has a small chance of error.
  • The AKS primality test always gives the correct answer in polynomial time, but is impractical due to slowness.
  • Fast methods are available for numbers of special forms, like Mersenne numbers.
  • The largest known prime number, as of October 2024, is a Mersenne prime with 41,024,320 decimal digits.

Distribution

  • Euclid demonstrated around 300 BC that there are infinitely many primes.
  • No simple formula exists to separate prime numbers from composite numbers.
  • The distribution of primes within natural numbers can be statistically modeled.
  • The prime number theorem, proven in the late 19th century, states that the probability of a large, randomly chosen number being prime is inversely proportional to its number of digits, relating to its logarithm.

Unsolved Problems

  • Goldbach's conjecture posits that every even integer greater than 2 can be expressed as the sum of two primes.
  • The twin prime conjecture suggests there are infinitely many pairs of primes that differ by two.
  • These questions have driven the development of analytic and algebraic aspects of number theory.

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