if $n = a_1a_2 cdots a_r + 2$, then $a_i nmid n$ for each integer $i (1 leq i leq r)$.












1












$begingroup$


Let $a_1, a_2, cdots , a_r$ be odd integers where $a_i > 1$ for $i = 1, 2, cdots , r$. Prove that if $n = a_1a_2 cdots a_r + 2$, then $a_i nmid n$ for each integer $i (1 leq i leq r)$.



Let $a_i mid n$, then $a_i mid a_1a_2 cdots a_r + 2$ also $a_i mid a_1a_2 cdots a_r$, thus $a_i mid a_1a_2 cdots a_r+2 - a_1a_2 cdots a_r implies a_i mid 2$, which is not possible since $a_i > 1$ is odd integer.



Is the logic correct?










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$endgroup$












  • $begingroup$
    Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
    $endgroup$
    – Bill Dubuque
    Nov 28 '18 at 19:38


















1












$begingroup$


Let $a_1, a_2, cdots , a_r$ be odd integers where $a_i > 1$ for $i = 1, 2, cdots , r$. Prove that if $n = a_1a_2 cdots a_r + 2$, then $a_i nmid n$ for each integer $i (1 leq i leq r)$.



Let $a_i mid n$, then $a_i mid a_1a_2 cdots a_r + 2$ also $a_i mid a_1a_2 cdots a_r$, thus $a_i mid a_1a_2 cdots a_r+2 - a_1a_2 cdots a_r implies a_i mid 2$, which is not possible since $a_i > 1$ is odd integer.



Is the logic correct?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
    $endgroup$
    – Bill Dubuque
    Nov 28 '18 at 19:38
















1












1








1





$begingroup$


Let $a_1, a_2, cdots , a_r$ be odd integers where $a_i > 1$ for $i = 1, 2, cdots , r$. Prove that if $n = a_1a_2 cdots a_r + 2$, then $a_i nmid n$ for each integer $i (1 leq i leq r)$.



Let $a_i mid n$, then $a_i mid a_1a_2 cdots a_r + 2$ also $a_i mid a_1a_2 cdots a_r$, thus $a_i mid a_1a_2 cdots a_r+2 - a_1a_2 cdots a_r implies a_i mid 2$, which is not possible since $a_i > 1$ is odd integer.



Is the logic correct?










share|cite|improve this question











$endgroup$




Let $a_1, a_2, cdots , a_r$ be odd integers where $a_i > 1$ for $i = 1, 2, cdots , r$. Prove that if $n = a_1a_2 cdots a_r + 2$, then $a_i nmid n$ for each integer $i (1 leq i leq r)$.



Let $a_i mid n$, then $a_i mid a_1a_2 cdots a_r + 2$ also $a_i mid a_1a_2 cdots a_r$, thus $a_i mid a_1a_2 cdots a_r+2 - a_1a_2 cdots a_r implies a_i mid 2$, which is not possible since $a_i > 1$ is odd integer.



Is the logic correct?







number-theory proof-verification divisibility integers






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edited Nov 28 '18 at 6:59









user26857

39.4k124183




39.4k124183










asked Nov 28 '18 at 6:11









user8795user8795

5,66462047




5,66462047












  • $begingroup$
    Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
    $endgroup$
    – Bill Dubuque
    Nov 28 '18 at 19:38




















  • $begingroup$
    Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
    $endgroup$
    – Bill Dubuque
    Nov 28 '18 at 19:38


















$begingroup$
Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
$endgroup$
– Bill Dubuque
Nov 28 '18 at 19:38






$begingroup$
Yes. Alternatively by Euclid $,gcd(n,a_i) = gcd(2,a_i) $ by $ 2 = nbmod a_i $
$endgroup$
– Bill Dubuque
Nov 28 '18 at 19:38












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        Yes, your reasoning is sound and correct.







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        answered Nov 28 '18 at 6:12









        plattyplatty

        3,370320




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