1. Use the fundamental theorem of arithmetic to show that every integer n > 2 can be written as a product n = s.r², where s, r > 1 are integers and s is square-free. We call this the square-free factorization. 2. For example, the square-free factorization of 8 = 2 · (2)² (s = 2, r = 2) and of 600 = 6 · 102 (s = 6, r = 10.) Find the square-free factorization of 72 and 2366. 3. Define S(N) = The number of squares between 1 and N F(N)= The number of square-free numbers between 1 and N What is S(4), S(25) and S(49)? F(6) and F(50)?
1. Use the fundamental theorem of arithmetic to show that every integer n > 2 can be written as a product n = s.r², where s, r > 1 are integers and s is square-free. We call this the square-free factorization. 2. For example, the square-free factorization of 8 = 2 · (2)² (s = 2, r = 2) and of 600 = 6 · 102 (s = 6, r = 10.) Find the square-free factorization of 72 and 2366. 3. Define S(N) = The number of squares between 1 and N F(N)= The number of square-free numbers between 1 and N What is S(4), S(25) and S(49)? F(6) and F(50)?
Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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
Transcribed Image Text:A lower bound for II(N).
In this question we will prove that there are infinitely many primes by examining the
prime counting function II(N), where
II(N) = The number of primes between 2 and N
We say that a natural number n > 2 is square-free if it is not divisible by a square.
For example, 6 is square-free, but 8 is not, since it is divisible by 4 = 22.
1. Use the fundamental theorem of arithmetic to show that every integer n > 2 can
be written as a product n = s·r², where s, r > 1 are integers and s is square-free.
We call this the square-free factorization.
2. For example, the square-free factorization of 8 = 2 · (2)² (s = 2,r = 2) and of
600 = 6 · 102 (s = 6,r = 10.) Find the square-free factorization of 72 and 2366.
3. Define
S(N) = The number of squares between 1 and N
F(N)
= The number of square-free numbers between 1 and N
What is S(4), S(25) and S(49)? F(6) and F(50)?
4. In part 1, we showed that every positive integer factors uniquely as a product of
a square and square-free number. Use this to conclude that N< S(N) · F(N).
In the next parts we'll overestimate both S(N) and F(N).
5. Show that S(N)< /N for every N > 1.
6. Show that F(N) < 2!(N). (Hint: every square free-number smaller than N of the
form q1 · q2 · ... · ¶k where the q¡ are distinct primes smaller than N.)
7. Now using 4, 5, and 6, we have N < VN · 2(N). Get II(N) by itself on the
right-hand side of this inequality.
8. Take the limit from the solved inequality in 6 to conclude that limN→ II(N) = ∞
and hence that there are infinitely many primes.
9. Using part 6, what's the smallest N guaranteed to have 500 primes smaller than
it?
10. What additional information does this proof provide that Euclid's doesn't?
This proof is due to Paul Erdos. There is a good documentary about him available to
watch by clicking here. Note that square/square-free numbers appear in the Elements.
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