Prime Numbers from 1 to 100

Prime numbers 1 to 100: there are 25 of them. Here they are in order: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97.

A prime number has exactly two factors, 1 and itself. In the chart below the prime numbers are highlighted, and every other number from 2 to 100 is composite.

How many prime numbers are there between 1 and 100?

The total is 25. Of these, 15 lie between 1 and 50 and 10 lie between 51 and 100. Only one of them is even, the number 2, so there are 24 odd prime numbers from 1 to 100. The other 74 numbers from 2 to 100 are composite, and 1 is neither prime nor composite.

Prime numbers 1 to 100 in groups of ten

Primes get a little rarer as numbers grow. Look at how many fall in each row of ten:

Prime numbers from 1 to 50

There are 15 prime numbers from 1 to 50: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47.

From 51 to 100 there are 10 primes: 53, 59, 61, 67, 71, 73, 79, 83, 89, 97. The largest prime number below 100 is 97. You can see how to write 97 in words and 97 in Roman numerals.

How to find prime numbers from 1 to 100: the sieve

The Sieve of Eratosthenes is the classic way to find every prime up to 100. It works like a filter.

1. Write the numbers 1 to 100 in a 10 by 10 grid. Cross out 1, since it is not prime.
2. Circle 2. Cross out every other multiple of 2: 4, 6, 8 and so on.
3. Circle 3. Cross out every multiple of 3 that is still left: 9, 15, 21 and so on.
4. Circle 5 and cross out its multiples. Then circle 7 and cross out its multiples. The first new one to go is 49, since 49 = 7 × 7.
5. Stop here. The next prime is 11, and 11 × 11 = 121 is already more than 100. Every number still not crossed out is prime.

This works because any composite number up to 100 must have a prime factor of 7 or less. The trickiest ones to catch are 49 (7 × 7), 77 (7 × 11) and 91 (7 × 13). The table of 7 helps here.

The same idea is used when you print prime numbers from 1 to 100 in Python, Java or C. The program loops through each number and tries to divide it by smaller numbers up to its square root. If nothing divides it, the number is printed.

Quick facts about prime numbers 1 to 100

• Sum of all prime numbers from 1 to 100: 1060.
• Smallest prime: 2. Largest prime below 100: 97.
• Odd prime numbers from 1 to 100: all 25 except 2, so 24.
• Twin prime pairs from 1 to 100: (3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), (71, 73). That is 8 pairs.
• Twin primes from 1 to 50: 6 pairs. From 51 to 100: (59, 61), (71, 73).
• The decade from 91 to 100 has only one prime, 97.

Prime numbers beyond 100

Primes keep going. Here are the counts for bigger ranges:

For the full list up to 1000, see prime numbers 1 to 1000. For the meaning of primes and how they differ from composite numbers, read our guide to prime numbers. Numbers like 8 and 15 are not prime but still have no common factor; those are co-prime numbers.

Check any number yourself with the prime checker: