Prime Numbers Eratosthenes’(ehr-uh-TAHS- thuh-neez) Sieve 276 BC - 194 BC •Eratosthenes was a Greek mathematician, astronomer, geographer, and librarian at Alexandria, Egypt in 200 B.C. • He invented a method for finding prime numbers that is still used today. • This method is called Eratosthenes’ Sieve.
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Prime Numbers Eratosthenes’ (ehr-uh-TAHS-thuh-neez) Sieve 276 BC - 194 BC Eratosthenes was a Greek mathematician, astronomer, geographer, and librarian.
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Prime NumbersEratosthenes’(ehr-uh-TAHS-thuh-
neez) Sieve
276 BC - 194 BC
•Eratosthenes was a Greek mathematician, astronomer, geographer, and librarian atAlexandria, Egypt in 200 B.C. •He invented a method for finding prime numbers that is still used today.•This method is called Eratosthenes’ Sieve.
Eratosthenes’ Sieve
A sieve has holes in it and is used to filter out the juice.
Eratosthenes’s sieve filters out numbers to find the prime numbers.
Definition
Factor – a number that is multiplied by another to give a product.
7 x 8 = 56
Factors
Definition
Prime Number – a number that has exactly two factors.
77 is prime because the only numbersthat will divide into it evenly are 1 and 7.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
Let’s use a number grid from 1 to 100 to see how prime numbers were discovered.
2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100
Remove the number 1. It is special number because 1 is its only factor.