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kkkk.tex
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kkkk.tex
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@ -105,7 +105,7 @@
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\include{luku28}
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\include{luku28}
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\include{luku29}
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\include{luku29}
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\include{luku30}
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\include{luku30}
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\include{kirj}
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%\include{kirj}
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\cleardoublepage
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\cleardoublepage
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\printindex
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\printindex
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luku21.tex
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luku21.tex
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@ -73,7 +73,7 @@ The factors are
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The \key{sum of factors} of $n$ is
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The \key{sum of factors} of $n$ is
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\[\sigma(n)=\prod_{i=1}^k (1+p_i+\ldots+p_i^{\alpha_i}) = \prod_{i=1}^k \frac{p_i^{a_i+1}-1}{p_i-1},\]
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\[\sigma(n)=\prod_{i=1}^k (1+p_i+\ldots+p_i^{\alpha_i}) = \prod_{i=1}^k \frac{p_i^{a_i+1}-1}{p_i-1},\]
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where the latter formula is based on the geometric sum formula.
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where the latter formula is based on the geometric progression formula.
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For example, the sum of factors of the number 84 is
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For example, the sum of factors of the number 84 is
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\[\sigma(84)=\frac{2^3-1}{2-1} \cdot \frac{3^2-1}{3-1} \cdot \frac{7^2-1}{7-1} = 7 \cdot 4 \cdot 8 = 224.\]
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\[\sigma(84)=\frac{2^3-1}{2-1} \cdot \frac{3^2-1}{3-1} \cdot \frac{7^2-1}{7-1} = 7 \cdot 4 \cdot 8 = 224.\]
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@ -89,7 +89,7 @@ and the product of the factors is $\mu(84)=84^6=351298031616$.
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\index{perfect number}
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\index{perfect number}
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A number $n$ is \key{perfect} if $n=\sigma(n)-n$,
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A number $n$ is \key{perfect} if $n=\sigma(n)-n$,
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i.e., $n$ equals the sum of its divisors
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i.e., $n$ equals the sum of its factors
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between $1$ and $n-1$.
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between $1$ and $n-1$.
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For example, the number 28 is perfect,
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For example, the number 28 is perfect,
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because $28=1+2+4+7+14$.
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because $28=1+2+4+7+14$.
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@ -355,10 +355,10 @@ For example,
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Numbers $a$ and $b$ are \key{coprime}
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Numbers $a$ and $b$ are \key{coprime}
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if $\textrm{gcd}(a,b)=1$.
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if $\textrm{gcd}(a,b)=1$.
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\key{Euler's totient function} $\varphi(n)$
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\key{Euler's totient function} $\varphi(n)$
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returns the number of coprime numbers to $n$
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gives the number of coprime numbers to $n$
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between $1$ and $n$.
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between $1$ and $n$.
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For example, $\varphi(12)=4$,
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For example, $\varphi(12)=4$,
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because the 1, 5, 7 and 11
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because 1, 5, 7 and 11
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are coprime to 12.
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are coprime to 12.
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The value of $\varphi(n)$ can be calculated
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The value of $\varphi(n)$ can be calculated
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@ -517,9 +517,9 @@ cout << x*x << "\n"; // 2537071545
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\index{Diophantine equation}
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\index{Diophantine equation}
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A \key{Diophantine equation} is of the form
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A \key{Diophantine equation} is an equation of the form
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\[ ax + by = c, \]
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\[ ax + by = c, \]
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where $a$, $b$ and $c$ are constants,
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where $a$, $b$ and $c$ are constants
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and we should find the values of $x$ and $y$.
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and we should find the values of $x$ and $y$.
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Each number in the equation has to be an integer.
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Each number in the equation has to be an integer.
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For example, one solution for the equation
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For example, one solution for the equation
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@ -575,10 +575,10 @@ and by multiplying this by 4, the result is
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\[
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\[
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39 \cdot 8 + 15 \cdot (-20) = 12,
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39 \cdot 8 + 15 \cdot (-20) = 12,
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\]
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\]
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so a solution for the equation is
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so a solution to the equation is
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$x=8$ and $y=-20$.
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$x=8$ and $y=-20$.
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A solution for a Diophantine equation is not unique,
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A solution to a Diophantine equation is not unique,
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but we can form an infinite number of solutions
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but we can form an infinite number of solutions
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if we know one solution.
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if we know one solution.
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If a pair $(x,y)$ is a solution, then also all pairs
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If a pair $(x,y)$ is a solution, then also all pairs
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@ -603,7 +603,7 @@ where all pairs of $m_1,m_2,\ldots,m_n$ are coprime.
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Let $x^{-1}_m$ be the inverse of $x$ modulo $m$, and
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Let $x^{-1}_m$ be the inverse of $x$ modulo $m$, and
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\[ X_k = \frac{m_1 m_2 \cdots m_n}{m_k}.\]
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\[ X_k = \frac{m_1 m_2 \cdots m_n}{m_k}.\]
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Using this notation, a solution for the equations is
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Using this notation, a solution to the equations is
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\[x = a_1 X_1 {X_1}^{-1}_{m_1} + a_2 X_2 {X_2}^{-1}_{m_2} + \cdots + a_n X_n {X_n}^{-1}_{m_n}.\]
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\[x = a_1 X_1 {X_1}^{-1}_{m_1} + a_2 X_2 {X_2}^{-1}_{m_2} + \cdots + a_n X_n {X_n}^{-1}_{m_n}.\]
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In this solution, it holds for each number
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In this solution, it holds for each number
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$k=1,2,\ldots,n$ that
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$k=1,2,\ldots,n$ that
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