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Thread: Standard notation

  1. #1
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    Question Standard notation

    Are these below a "standard" (i.e. not-obscure) piece one can see in textbooks:

    $\displaystyle n_{(r)}=\frac{n^{(r)}}{r!}$ [$\displaystyle n_{(3)}=\frac{n(n-1)(n-2)}{3!}$] and $\displaystyle n_{r}=\frac{n^r}{r!}$

    ($\displaystyle n!!$, I presume, is "standard".)

    Pretty please post more "alike".
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  2. #2
    Senior Member apcalculus's Avatar
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    Quote Originally Posted by courteous View Post
    Are these below a "standard" (i.e. not-obscure) piece one can see in textbooks:

    $\displaystyle n_{(r)}=\frac{n^{(r)}}{r!}$ [$\displaystyle n_{(3)}=\frac{n(n-1)(n-2)}{3!}$] and $\displaystyle n_{r}=\frac{n^r}{r!}$

    ($\displaystyle n!!$, I presume, is "standard".)

    Pretty please post more "alike".
    The factorial notation is "standard", sure. Sorry, I may be missing the point here. Are you asking if this notation is typical?
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  3. #3
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    I am not sure I've seen the subscript and superscript notation.
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  4. #4
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    Quote Originally Posted by emakarov View Post
    I am not sure I've seen the subscript and superscript notation.
    I definitely agree with that.

    It appears to me as if the is a combination of the standard usage of permutations and factorials.
    By that I mean $\displaystyle _n\mathcal{P}_j=\frac{n!}{(n-j)!}$ so that $\displaystyle _{10}\mathcal{P}_3=(10)(9)(7) $.

    So that $\displaystyle n_{(r)}=\frac{_n\mathcal{P}_r }{r!}$.
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