Cyclotomic Polynomial of Prime Index
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Theorem
Let $p$ be a prime number.
The $p$th cyclotomic polynomial is:
- $\map {\Phi_p} x = x^{p - 1} + x^{p - 2} + \cdots + x + 1$
Proof
From Product of Cyclotomic Polynomials:
- $\map {\Phi_p} x \map {\Phi_1} x = x^p - 1$
Thus from Sum of Geometric Sequence:
- $\map {\Phi_p} x = \dfrac {x^p - 1} {x - 1} = x^{p - 1} + x^{p - 2} + \cdots + x + 1$
$\blacksquare$