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The sequence 2, 3, 5, 6, 7, 10, 11,  contains all the positive integers from least to greatest that are neither squares nor cubes. What is the \(400^{\mathrm{th}}\) term of the sequence?

Logic  Oct 12, 2018
 #1
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I'm seeing it's 425.

 

I don't have a suggestion on how to find that though.

 

I guess you could start at 400 and add 1 for every square or cube you encounter in the list

 

There are 20 squares <= 400, 1-20,

There are 7 cubes <= 400, 1-7

 

But you seem to be excluding 1 from the series and that's counted here twice so we only have 25 squares and cubes.

 

Thus the 400th element is 425.

Rom  Oct 12, 2018
edited by Rom  Oct 12, 2018
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I think it is: OEIS A003754

Guest Oct 12, 2018

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