Max order of an isogeny class of rational elliptic curves is 8?For which composite $N$ does $X_0(N)$ possess a non-cuspidal rational point?About isogeny theorem for elliptic curvesMust the $j$-invariant of an elliptic curve with an isogeny be integral?Elliptic curves over QQ with isomorphic n-torsion$j$-invariants of elliptic curves over finite fieldstwists of elliptic curves over finite fields

Max order of an isogeny class of rational elliptic curves is 8?


For which composite $N$ does $X_0(N)$ possess a non-cuspidal rational point?About isogeny theorem for elliptic curvesMust the $j$-invariant of an elliptic curve with an isogeny be integral?Elliptic curves over QQ with isomorphic n-torsion$j$-invariants of elliptic curves over finite fieldstwists of elliptic curves over finite fields













8












$begingroup$


I am looking for a reference for the proof of the following question following Theorem 5 in Mazur's Rational Isogenies of Prime Degree.



Theorem 5 There is a constant $C$ such that every elliptic curve $E_/mathbbQ$ is isogenous (over $mathbbQ$) to at most $C$ (mutually nonisomorphic) elliptic curves.



"Can one take $C=8$?"



Has this question been settled? And if so, what is a reference to the proof of the result.










share|cite|improve this question











$endgroup$


















    8












    $begingroup$


    I am looking for a reference for the proof of the following question following Theorem 5 in Mazur's Rational Isogenies of Prime Degree.



    Theorem 5 There is a constant $C$ such that every elliptic curve $E_/mathbbQ$ is isogenous (over $mathbbQ$) to at most $C$ (mutually nonisomorphic) elliptic curves.



    "Can one take $C=8$?"



    Has this question been settled? And if so, what is a reference to the proof of the result.










    share|cite|improve this question











    $endgroup$
















      8












      8








      8


      1



      $begingroup$


      I am looking for a reference for the proof of the following question following Theorem 5 in Mazur's Rational Isogenies of Prime Degree.



      Theorem 5 There is a constant $C$ such that every elliptic curve $E_/mathbbQ$ is isogenous (over $mathbbQ$) to at most $C$ (mutually nonisomorphic) elliptic curves.



      "Can one take $C=8$?"



      Has this question been settled? And if so, what is a reference to the proof of the result.










      share|cite|improve this question











      $endgroup$




      I am looking for a reference for the proof of the following question following Theorem 5 in Mazur's Rational Isogenies of Prime Degree.



      Theorem 5 There is a constant $C$ such that every elliptic curve $E_/mathbbQ$ is isogenous (over $mathbbQ$) to at most $C$ (mutually nonisomorphic) elliptic curves.



      "Can one take $C=8$?"



      Has this question been settled? And if so, what is a reference to the proof of the result.







      nt.number-theory reference-request elliptic-curves






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Aug 11 at 19:37









      YCor

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      31k4 gold badges95 silver badges147 bronze badges










      asked Aug 10 at 13:51









      ABarriosABarrios

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      1237 bronze badges























          1 Answer
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          $begingroup$

          M. Kenku, On the number of $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny
          class, J. Number Theory 15, 199 (1982):
          It is shown that there are at most eight $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny class.






          share|cite|improve this answer











          $endgroup$














          • $begingroup$
            Thank you, Carlo!
            $endgroup$
            – ABarrios
            Aug 10 at 14:21













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          1 Answer
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          13













          $begingroup$

          M. Kenku, On the number of $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny
          class, J. Number Theory 15, 199 (1982):
          It is shown that there are at most eight $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny class.






          share|cite|improve this answer











          $endgroup$














          • $begingroup$
            Thank you, Carlo!
            $endgroup$
            – ABarrios
            Aug 10 at 14:21















          13













          $begingroup$

          M. Kenku, On the number of $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny
          class, J. Number Theory 15, 199 (1982):
          It is shown that there are at most eight $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny class.






          share|cite|improve this answer











          $endgroup$














          • $begingroup$
            Thank you, Carlo!
            $endgroup$
            – ABarrios
            Aug 10 at 14:21













          13














          13










          13







          $begingroup$

          M. Kenku, On the number of $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny
          class, J. Number Theory 15, 199 (1982):
          It is shown that there are at most eight $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny class.






          share|cite|improve this answer











          $endgroup$



          M. Kenku, On the number of $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny
          class, J. Number Theory 15, 199 (1982):
          It is shown that there are at most eight $mathbfQ$-isomorphism classes of elliptic curves in each $mathbfQ$-isogeny class.







          share|cite|improve this answer














          share|cite|improve this answer



          share|cite|improve this answer








          edited Aug 11 at 19:38









          YCor

          31k4 gold badges95 silver badges147 bronze badges




          31k4 gold badges95 silver badges147 bronze badges










          answered Aug 10 at 14:18









          Carlo BeenakkerCarlo Beenakker

          86.6k9 gold badges208 silver badges314 bronze badges




          86.6k9 gold badges208 silver badges314 bronze badges














          • $begingroup$
            Thank you, Carlo!
            $endgroup$
            – ABarrios
            Aug 10 at 14:21
















          • $begingroup$
            Thank you, Carlo!
            $endgroup$
            – ABarrios
            Aug 10 at 14:21















          $begingroup$
          Thank you, Carlo!
          $endgroup$
          – ABarrios
          Aug 10 at 14:21




          $begingroup$
          Thank you, Carlo!
          $endgroup$
          – ABarrios
          Aug 10 at 14:21

















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