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Student Support Forum: 'Solving for when a summation reaches a value.' topicStudent Support Forum > General > Archives > "Solving for when a summation reaches a value."

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Author Comment/Response
JD
07/08/13 6:42pm

In Response To 'Re: Solving for when a summation reaches a value.'
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I tried it on my computer and the graph I came up with is a simple x=y graph. Maybe if the y side of the graph was the LCM (1,2,...n)and the x side of the graph was n, I could get a ballpark estimate.

I looked into the reference you gave for Mathworld. I had been there long ago, but I did see that

Psi(n)= ln(LCM(1,2,3,...,n)

so if I understand logs correctly, then

E^[Psi(n)]= (LCM(1,2,3,...,n)

and then the following should give me the number of digits of the LCM

In[]:= Solve[3 <= Ceiling[log[E^(\[Psi] (n))]] && n > 0, n ][[1]]

During evaluation of In[]:=
Solve::nsmet : "This system cannot be solved with the methods \
available to Solve. \!\(\*ButtonBox["\[RightSkeleton]",
Appearance->{Automatic, None},
BaseStyle->"Link",
ButtonData:>"paclet:ref/Solve",
ButtonNote->"Solve::nsmet"]\)"

Out[]= 3 <= Ceiling[log[E^(n \[Psi])]] && n > 0


Ceiling[log[E^(\[Psi] (9))]]

During evaluation of In[38]:=
Syntax::tsntxi : "\"\[NoBreak][Ceiling[log[\[ExponentialE]^(\[Psi] \
(9))]]]\[NoBreak]\" is incomplete; more input is needed.\[NoBreak]""\
\[NoBreak]"

During evaluation of In[38]:=
Syntax::sntxi : "Incomplete expression; more input is needed \
\[NoBreak]""\[NoBreak]."

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Okay, so I'm giving the computer really simply stuff and it just gives it back to me with the last entry.
Since I am so new to Mathematica, I assume that there has to be something completely basic that I am not doing.
I can't even get it to

Evaluate[^(y(9))]

I am using a notebook, .nb file. I right click on the cell after I'm finished and use Evaluate Cell. Nothing is happening.
I should have got an answer of e^2520 or some number. If this thing doesn't put out soon, I'm going to explode.


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Subject (listing for 'Solving for when a summation reaches a value.')
Author Date Posted
Solving for when a summation reaches a value. JD 07/08/13 06:54am
Re: Solving for when a summation reaches a value. Bill Simpson 07/08/13 4:36pm
Re: Re: Solving for when a summation reaches a ... JD 07/08/13 6:42pm
Re: Solving for when a summation reaches a value. Bill Simpson 07/09/13 01:15am
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