algebra

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What is the least positive interger n such that 3n - n3 is an even 4 digit #.
 
You can start with
3N-N^3=1000
to get the smalles possible N that gives any four digit number.

BTW Soroban. Ya can't skip the even numbers. They work too.
 
Hello, Ashley Cook!

First of all, I'll take a flying guess at what you meant . . .
\(\displaystyle \;\;\)(Edit: I see that Gene is on the same wavelength.)

What is the least positive interger \(\displaystyle n\) such that \(\displaystyle \,3^n\,-\,n^3\) is an even 4-digit number.
Second, what techniques are available to you?
\(\displaystyle \;\;\)Graphing? \(\displaystyle \;\)modulo artihmetic? \(\displaystyle \;\) trial-and-error?

I noted that \(\displaystyle 3^n\) is an odd number\(\displaystyle \;\;\Rightarrow\;\;n^3\) must be odd\(\displaystyle \;\;\Rightarrow\;\;n\) is odd.

Then try: \(\displaystyle \,n\:=\:1,\,3,\,5,\,7,\,\cdots\)
 
Yup, same wavelength all the way thru, but from the equation n³-3n=1000, n=10 is very close to the thousand so 11 is the first number to try and the analysis says it will work.
 
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