What are the positive integral solution sets of $a^2+ab+b^2=343k$?












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I had encountered a problem in which we had to find all positive integers $(a,b,k)$ such that $a^2+ab+b^2=343k$. I had never had a general approach to solve such an equation having three variables. Would someone please help me to solve this equation?










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  • 5




    $begingroup$
    Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
    $endgroup$
    – Aravind
    Jan 26 at 17:42
















1












$begingroup$


I had encountered a problem in which we had to find all positive integers $(a,b,k)$ such that $a^2+ab+b^2=343k$. I had never had a general approach to solve such an equation having three variables. Would someone please help me to solve this equation?










share|cite|improve this question









$endgroup$








  • 5




    $begingroup$
    Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
    $endgroup$
    – Aravind
    Jan 26 at 17:42














1












1








1


2



$begingroup$


I had encountered a problem in which we had to find all positive integers $(a,b,k)$ such that $a^2+ab+b^2=343k$. I had never had a general approach to solve such an equation having three variables. Would someone please help me to solve this equation?










share|cite|improve this question









$endgroup$




I had encountered a problem in which we had to find all positive integers $(a,b,k)$ such that $a^2+ab+b^2=343k$. I had never had a general approach to solve such an equation having three variables. Would someone please help me to solve this equation?







number-theory






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asked Jan 26 at 17:34









Shashwat1337Shashwat1337

959




959








  • 5




    $begingroup$
    Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
    $endgroup$
    – Aravind
    Jan 26 at 17:42














  • 5




    $begingroup$
    Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
    $endgroup$
    – Aravind
    Jan 26 at 17:42








5




5




$begingroup$
Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
$endgroup$
– Aravind
Jan 26 at 17:42




$begingroup$
Hint: Write this as $a^3 equiv b^3$ mod 343 and $a neq b$ mod 343. Also $343=7^3.$
$endgroup$
– Aravind
Jan 26 at 17:42










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