Proving the Irreducibility of Multinacci Polynomial g(x) for Natural Numbers m

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The discussion focuses on proving the irreducibility of the Multinacci polynomial g(x) = x^m - x^{m-1} - x^{m-2} - ... - x - 1 over the rationals for all natural numbers m. A proposed method involves using an evaluation homomorphism, specifically φ_{x+1}, to transform the polynomial and applying the Eisenstein criterion. However, it is noted that the Eisenstein criterion does not universally apply for all values of m, as demonstrated with the example of m=4, where the transformed polynomial does not yield a suitable prime.

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Diophantus
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Can anyone please give me a hint on how I can prove that

[tex]g(x) = x^m - x^{m-1} - x^{m-2} - ... - x - 1[/tex]

is irreudicble over the rationals for all natural numbers m?

Regards
 
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I would use an evaluation homomorphism, to change the variable, and then use the Eisenstein criterion for a prime p and show it is irreducible. I haven't actually done it (so this might be wrong), but this is what I would try first.

The evaluation homomorphism I would use would be of the form

[tex]\phi_{x+1}\,:\,\mathbb{Q}[x] \rightarrow \mathbb{Q}[x] \quad\quad \phi_{x+1}(g(x)) = g(x+1)[/tex]

Hopefully you'll get a nice binomial expression to which you can check if p divides (by Eisenstein's Criteria).
 
Alas, the Eisenstein criteria will not work here for every m.

Indeed [tex]\phi_{x+1}(x^4 - x^3 - x^2 - x - 1) = x^4 + 3x^3 + 2x^2 - 2x - 3[/tex]

and then (2,3) = 1 implies that no suitable prime can be found.

Any other ideas?
 

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