More about odd numbers in Pascal's triangle












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Do you have any references to this interesting result? I could not find any...



The total number of odd numbers in the first $2^n$ rows of Pascal's triangle is $3^n$, $n>=0$.



It's easy to prove by induction based on the formula for the number of odds in row $n$ ($2^m$, where $m$ is the number of ones in the binary expansion of $n$).










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  • $begingroup$
    Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
    $endgroup$
    – Mircea Draghicescu
    Jan 29 at 22:10
















1












$begingroup$


Do you have any references to this interesting result? I could not find any...



The total number of odd numbers in the first $2^n$ rows of Pascal's triangle is $3^n$, $n>=0$.



It's easy to prove by induction based on the formula for the number of odds in row $n$ ($2^m$, where $m$ is the number of ones in the binary expansion of $n$).










share|cite|improve this question









$endgroup$












  • $begingroup$
    Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
    $endgroup$
    – Mircea Draghicescu
    Jan 29 at 22:10














1












1








1





$begingroup$


Do you have any references to this interesting result? I could not find any...



The total number of odd numbers in the first $2^n$ rows of Pascal's triangle is $3^n$, $n>=0$.



It's easy to prove by induction based on the formula for the number of odds in row $n$ ($2^m$, where $m$ is the number of ones in the binary expansion of $n$).










share|cite|improve this question









$endgroup$




Do you have any references to this interesting result? I could not find any...



The total number of odd numbers in the first $2^n$ rows of Pascal's triangle is $3^n$, $n>=0$.



It's easy to prove by induction based on the formula for the number of odds in row $n$ ($2^m$, where $m$ is the number of ones in the binary expansion of $n$).







combinatorics binomial-coefficients






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asked Jan 29 at 19:50









Mircea DraghicescuMircea Draghicescu

184




184












  • $begingroup$
    Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
    $endgroup$
    – Mircea Draghicescu
    Jan 29 at 22:10


















  • $begingroup$
    Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
    $endgroup$
    – Mircea Draghicescu
    Jan 29 at 22:10
















$begingroup$
Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
$endgroup$
– Mircea Draghicescu
Jan 29 at 22:10




$begingroup$
Just saw it: the answer by @Micah to the "Odds in Pascal's Triangle" post includes a direct proof of this fact.
$endgroup$
– Mircea Draghicescu
Jan 29 at 22:10










1 Answer
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$begingroup$

The Online Encyclopedia of Integer Sequences lists as entry A006046




Total number of odd entries in first n rows of Pascal's triangle: a(0) = 0, a(1) = 1, a(2k) = 3*a(k), a(2k+1) = 2*a(k) + a(k+1)




which doesn't give the claim explicitly but makes it very clear implicitly. Further down, in the formula section, you can find it explicitly:




a(2^n) = 3^n. - Henry Bottomley, Apr 05 2001







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    1 Answer
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    $begingroup$

    The Online Encyclopedia of Integer Sequences lists as entry A006046




    Total number of odd entries in first n rows of Pascal's triangle: a(0) = 0, a(1) = 1, a(2k) = 3*a(k), a(2k+1) = 2*a(k) + a(k+1)




    which doesn't give the claim explicitly but makes it very clear implicitly. Further down, in the formula section, you can find it explicitly:




    a(2^n) = 3^n. - Henry Bottomley, Apr 05 2001







    share|cite|improve this answer









    $endgroup$


















      1












      $begingroup$

      The Online Encyclopedia of Integer Sequences lists as entry A006046




      Total number of odd entries in first n rows of Pascal's triangle: a(0) = 0, a(1) = 1, a(2k) = 3*a(k), a(2k+1) = 2*a(k) + a(k+1)




      which doesn't give the claim explicitly but makes it very clear implicitly. Further down, in the formula section, you can find it explicitly:




      a(2^n) = 3^n. - Henry Bottomley, Apr 05 2001







      share|cite|improve this answer









      $endgroup$
















        1












        1








        1





        $begingroup$

        The Online Encyclopedia of Integer Sequences lists as entry A006046




        Total number of odd entries in first n rows of Pascal's triangle: a(0) = 0, a(1) = 1, a(2k) = 3*a(k), a(2k+1) = 2*a(k) + a(k+1)




        which doesn't give the claim explicitly but makes it very clear implicitly. Further down, in the formula section, you can find it explicitly:




        a(2^n) = 3^n. - Henry Bottomley, Apr 05 2001







        share|cite|improve this answer









        $endgroup$



        The Online Encyclopedia of Integer Sequences lists as entry A006046




        Total number of odd entries in first n rows of Pascal's triangle: a(0) = 0, a(1) = 1, a(2k) = 3*a(k), a(2k+1) = 2*a(k) + a(k+1)




        which doesn't give the claim explicitly but makes it very clear implicitly. Further down, in the formula section, you can find it explicitly:




        a(2^n) = 3^n. - Henry Bottomley, Apr 05 2001








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        share|cite|improve this answer










        answered Jan 29 at 22:11









        Peter TaylorPeter Taylor

        9,15712343




        9,15712343






























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