# Basics of Prime Numbers: Definition, Chart, Properties, and Solved Examples

Prime numbers, fundamental to number theory, are the building blocks of the number system. A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. For example, 2, 3, 5, and 7 are all prime numbers. This unique property makes them integral to various mathematical concepts and applications. Understanding prime numbers involves exploring their properties, such as their indivisibility and the fact that every number greater than 1 is either a prime or can be factored into primes. This guide delves into the basics of prime numbers, presenting a chart of primes, discussing their important properties, and providing solved examples to illustrate their practical applications.

## Definition of Prime Numbers?

A prime number is a natural number greater than 1 that has no positive divisors other than 1 and itself. In other words, a prime number cannot be formed by multiplying two smaller natural numbers. For example, 2, 3, 5, and 7 are prime numbers because they can only be divided evenly by 1 and themselves. Conversely, numbers like 4, 6, and 8 are not prime because they can be divided evenly by numbers other than 1 and themselves (e.g., 4 can be divided by 2, 6 by 2 and 3, and 8 by 2 and 4).

Properties of Prime Numbers:

• Indivisibility: A prime number is only divisible by 1 and itself. For example, 7 can only be divided by 1 and 7 without leaving a remainder.
• Uniqueness: Every natural number greater than 1 is either a prime number or can be factored uniquely into prime numbers. This is known as the Fundamental Theorem of Arithmetic.
• First Prime Number: The smallest prime number is 2. It is also the only even prime number because any other even number can be divided by 2, making it not prime.
• Distribution: Prime numbers become less frequent as numbers get larger, but there are infinitely many prime numbers.
• Primality Testing: Determining whether a large number is prime is more complex and requires special algorithms, such as the Sieve of Eratosthenes or probabilistic tests for very large numbers.
• Prime Gaps: The difference between consecutive prime numbers is called a prime gap. As numbers increase, these gaps can become larger, but they can also be as small as 2, known as twin primes (e.g., 11 and 13).

## Chart of Prime Numbers

Here is a chart listing the first 50 prime numbers:

## Properties of Prime Numbers with Formulas

Prime numbers have several important properties, each often accompanied by specific formulas or characteristics. Here are some key properties along with relevant formulas:

Divisibility:

• A prime number ppp is only divisible by 1 and ppp itself.
• For example, 7 is a prime number because its only divisors are 1 and 7.

Uniqueness in Factorization:

• Every integer greater than 1 is either a prime or can be uniquely expressed as a product of prime numbers (this is known as the Fundamental Theorem of Arithmetic).
• For example, 30 can be factored into prime numbers as 2×3×5.

Smallest Prime Number:

• The smallest and only even prime number is 2.
• All other even numbers are not prime because they can be divided by 2.

Prime Gaps:

• The difference between consecutive prime numbers varies and can sometimes be large.
• For example, the gap between 3 and 5 is 2, but the gap between 23 and 29 is 6.

Twin Primes:

• Twin primes are pairs of prime numbers that have a difference of 2.
• Examples include (11, 13) and (17, 19).

## Properties of Prime Numbers with Solved Examples

Here are five solved examples involving prime numbers.

Q1: Determine if 29 is a prime number.

Solution:

1. A prime number has no divisors other than 1 and itself.
2. Check divisibility by all integers from 2 to 29.
3. 29 is not divisible by 2, 3, or 5.

Since 29 is not divisible by any number other than 1 and 29, it is a prime number.

Q2: Find the prime factorization of 60.

Solution:

1. Divide 60 by the smallest prime number (2): 60÷2=30.
2. Divide 30 by 2: 30÷2=15.
3. Divide 15 by the next smallest prime number (3): 15÷3=5
4. 5 is a prime number.

The prime factorization of 60 is 2×2×3×5.

Q3: List all prime numbers between 10 and 20.

Solution:

1. Check each number from 11 to 19 for primality:
• 11: Prime (divisors 1 and 11)
• 12: Not prime (divisors 1, 2, 3, 4, 6, 12)
• 13: Prime (divisors 1 and 13)
• 14: Not prime (divisors 1, 2, 7, 14)
• 15: Not prime (divisors 1, 3, 5, 15)
• 16: Not prime (divisors 1, 2, 4, 8, 16)
• 17: Prime (divisors 1 and 17)
• 18: Not prime (divisors 1, 2, 3, 6, 9, 18)
• 19: Prime (divisors 1 and 19)

The prime numbers between 10 and 20 are 11, 13, 17, and 19.

Q4: Find the sum of the first 5 prime numbers.

Solution:

1. The first 5 prime numbers are 2, 3, 5, 7, and 11.
2. Sum = 2+3+5+7+11=28.

The sum of the first 5 prime numbers is 28.

Q5: Determine if 77 is the product of two prime numbers.

Solution:

1. Check for factors of 77:
• 77 is not divisible by 2, 3, or 5.
• 77 is divisible by 7: 77÷7=11
• Both 7 and 11 are prime numbers.

77 is the product of the prime numbers 7 and 11.

## FAQs

What makes a prime number?

Any natural number that can only be divided by itself and one is a prime number. That is, prime numbers are whole numbers that are bigger than 1 and have only one part, which is the number itself. The prime numbers are 2, 3, 5, 7, 11, 13, and so on.

What are the rules for prime numbers?

Prime numbers are those that can only be divided by themselves and 1. If you try to divide them by another number, you get a non-whole number. What this means is that if you split the number by something other than one or itself, you will get a number besides zero.

Why is 2 the smallest prime number?

There can be only two factors of a prime number: 1 and the number itself. Since only 1 and 2 can be divided by 2, the number 2 is the lowest prime number.

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