Multiples of triangular numbers












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I know that $;2T_2=T_3;$ is a triangular number.

Can anyone suggest me other triangular numbers whose two multiple is again a triangular number?










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  • $begingroup$
    Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
    $endgroup$
    – Matti P.
    Jan 22 at 8:41








  • 4




    $begingroup$
    See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:42






  • 1




    $begingroup$
    Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
    $endgroup$
    – José Carlos Santos
    Jan 22 at 8:43










  • $begingroup$
    Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
    $endgroup$
    – Matti P.
    Jan 22 at 8:44












  • $begingroup$
    See also oeis.org/A029549
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:44
















0












$begingroup$


I know that $;2T_2=T_3;$ is a triangular number.

Can anyone suggest me other triangular numbers whose two multiple is again a triangular number?










share|cite|improve this question











$endgroup$












  • $begingroup$
    Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
    $endgroup$
    – Matti P.
    Jan 22 at 8:41








  • 4




    $begingroup$
    See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:42






  • 1




    $begingroup$
    Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
    $endgroup$
    – José Carlos Santos
    Jan 22 at 8:43










  • $begingroup$
    Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
    $endgroup$
    – Matti P.
    Jan 22 at 8:44












  • $begingroup$
    See also oeis.org/A029549
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:44














0












0








0





$begingroup$


I know that $;2T_2=T_3;$ is a triangular number.

Can anyone suggest me other triangular numbers whose two multiple is again a triangular number?










share|cite|improve this question











$endgroup$




I know that $;2T_2=T_3;$ is a triangular number.

Can anyone suggest me other triangular numbers whose two multiple is again a triangular number?







real-numbers






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Jan 22 at 9:03









user376343

3,9234829




3,9234829










asked Jan 22 at 8:35









AnuAnu

1




1












  • $begingroup$
    Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
    $endgroup$
    – Matti P.
    Jan 22 at 8:41








  • 4




    $begingroup$
    See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:42






  • 1




    $begingroup$
    Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
    $endgroup$
    – José Carlos Santos
    Jan 22 at 8:43










  • $begingroup$
    Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
    $endgroup$
    – Matti P.
    Jan 22 at 8:44












  • $begingroup$
    See also oeis.org/A029549
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:44


















  • $begingroup$
    Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
    $endgroup$
    – Matti P.
    Jan 22 at 8:41








  • 4




    $begingroup$
    See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:42






  • 1




    $begingroup$
    Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
    $endgroup$
    – José Carlos Santos
    Jan 22 at 8:43










  • $begingroup$
    Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
    $endgroup$
    – Matti P.
    Jan 22 at 8:44












  • $begingroup$
    See also oeis.org/A029549
    $endgroup$
    – Mark Bennet
    Jan 22 at 8:44
















$begingroup$
Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
$endgroup$
– Matti P.
Jan 22 at 8:41






$begingroup$
Hint: Triangular numbers in general are of the form $$ T_n = frac{n(n+1)}{2} $$ So if you have $2T_r = T_s$ for some pair $(r,s)$, what are their possible values?
$endgroup$
– Matti P.
Jan 22 at 8:41






4




4




$begingroup$
See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
$endgroup$
– Mark Bennet
Jan 22 at 8:42




$begingroup$
See this near duplicate math.stackexchange.com/questions/2075913/…. You get a Pell equation.
$endgroup$
– Mark Bennet
Jan 22 at 8:42




1




1




$begingroup$
Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
$endgroup$
– José Carlos Santos
Jan 22 at 8:43




$begingroup$
Welcome to MSE. You should choose your tags carefully. What has this to do with real-numbers?
$endgroup$
– José Carlos Santos
Jan 22 at 8:43












$begingroup$
Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
$endgroup$
– Matti P.
Jan 22 at 8:44






$begingroup$
Another pair is $(14,20)$. And $(84,119)$, $(494,696)$ ...
$endgroup$
– Matti P.
Jan 22 at 8:44














$begingroup$
See also oeis.org/A029549
$endgroup$
– Mark Bennet
Jan 22 at 8:44




$begingroup$
See also oeis.org/A029549
$endgroup$
– Mark Bennet
Jan 22 at 8:44










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