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Questions and Answers
What is a divisor of a number?
What is a divisor of a number?
What is a prime number?
What is a prime number?
What is the purpose of the Euclidean Algorithm?
What is the purpose of the Euclidean Algorithm?
What does the symbol ≡ mean in a congruence?
What does the symbol ≡ mean in a congruence?
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What is a Diophantine equation?
What is a Diophantine equation?
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What does Fermat's Little Theorem state?
What does Fermat's Little Theorem state?
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What is the Fundamental Theorem of Arithmetic?
What is the Fundamental Theorem of Arithmetic?
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What is a property of the GCD of two integers?
What is a property of the GCD of two integers?
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Study Notes
Divisibility
- A divisor of a number is an integer that divides it without leaving a remainder.
- Notation:
a | b
means "a divides b" or "a is a divisor of b". - Properties:
- If
a | b
anda | c
, thena | (b + c)
. - If
a | b
anda | c
, thena | (b - c)
. - If
a | b
andc | a
, thenc | b
.
- If
Prime Numbers
- A prime number is a positive integer greater than 1 that is divisible only by 1 and itself.
- Examples: 2, 3, 5, 7, 11, ...
- Properties:
- There are infinitely many prime numbers.
- Every positive integer can be expressed as a product of prime numbers in a unique way ( Fundamental Theorem of Arithmetic).
Greatest Common Divisor (GCD)
- The GCD of two or more integers is the largest integer that divides each of them without leaving a remainder.
- Notation:
gcd(a, b)
or(a, b)
. - Properties:
-
gcd(a, b) = gcd(b, a)
. -
gcd(a, b) = gcd(a, b + a)
. -
gcd(a, b) = gcd(a, b - a)
.
-
Euclidean Algorithm
- A method for computing the GCD of two integers.
- Steps:
- Divide the larger number by the smaller number.
- Take the remainder as the new smaller number.
- Repeat steps 1 and 2 until the remainder is 0.
- The last non-zero remainder is the GCD.
Congruences
- A congruence is an equation of the form
a ≡ b (mod n)
, wherea
,b
, andn
are integers. - Meaning:
a
andb
have the same remainder when divided byn
. - Properties:
-
a ≡ a (mod n)
. - If
a ≡ b (mod n)
, thenb ≡ a (mod n)
. - If
a ≡ b (mod n)
andb ≡ c (mod n)
, thena ≡ c (mod n)
.
-
Diophantine Equations
- A linear Diophantine equation is an equation of the form
ax + by = c
, wherea
,b
, andc
are integers. - Solution:
x = x0 + (b/d)t
,y = y0 - (a/d)t
, whered = gcd(a, b)
andx0
,y0
are particular solutions.
Fermat's Little Theorem
- If
p
is a prime number, thena^p ≡ a (mod p)
for any integera
. - Corollary: If
p
is a prime number, thena^(p-1) ≡ 1 (mod p)
for any integera
not divisible byp
.
Divisibility
- A divisor is an integer that divides another integer without leaving a remainder.
- Notation:
a | b
means "a divides b" or "a is a divisor of b". - Properties of divisibility:
- If
a
dividesb
anda
dividesc
, thena
dividesb + c
. - If
a
dividesb
anda
dividesc
, thena
dividesb - c
. - If
a
dividesb
andc
dividesa
, thenc
dividesb
.
- If
Prime Numbers
- A prime number is a positive integer greater than 1 that is divisible only by 1 and itself.
- Examples: 2, 3, 5, 7, 11, ...
- Properties of prime numbers:
- There are infinitely many prime numbers.
- Every positive integer can be expressed as a product of prime numbers in a unique way (Fundamental Theorem of Arithmetic).
Greatest Common Divisor (GCD)
- The GCD of two or more integers is the largest integer that divides each of them without leaving a remainder.
- Notation:
gcd(a, b)
or(a, b)
. - Properties of GCD:
-
gcd(a, b) = gcd(b, a)
. -
gcd(a, b) = gcd(a, b + a)
. -
gcd(a, b) = gcd(a, b - a)
.
-
Euclidean Algorithm
- A method for computing the GCD of two integers using repeated divisions.
- Steps:
- Divide the larger number by the smaller number.
- Take the remainder as the new smaller number.
- Repeat steps until the remainder is 0.
- The last non-zero remainder is the GCD.
Congruences
- A congruence is an equation of the form
a ≡ b (mod n)
, wherea
,b
, andn
are integers. - Meaning:
a
andb
have the same remainder when divided byn
. - Properties of congruences:
-
a ≡ a (mod n)
. - If
a ≡ b (mod n)
, thenb ≡ a (mod n)
. - If
a ≡ b (mod n)
andb ≡ c (mod n)
, thena ≡ c (mod n)
.
-
Diophantine Equations
- A linear Diophantine equation is an equation of the form
ax + by = c
, wherea
,b
, andc
are integers. - Solution:
x = x0 + (b/d)t
,y = y0 - (a/d)t
, whered = gcd(a, b)
andx0
,y0
are particular solutions.
Fermat's Little Theorem
- If
p
is a prime number, thena^p ≡ a (mod p)
for any integera
. - Corollary: If
p
is a prime number, thena^(p-1) ≡ 1 (mod p)
for any integera
not divisible byp
.
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Description
Explore the basics of number theory, including divisors, prime numbers, and their properties. Learn to identify divisors, understand prime numbers, and discover their characteristics.