On the Galois groups of the exponential Taylor polynomials. (English) Zbl 0672.12004

Coleman, Robert F.

Enseign. Math., II. Sér. 33, 183-189 (1987).

Let \(f_ n(X)\) be the polynomial \(1+x+x^ 2/2!+\dots+x^ n/n!\) over \({\mathbb{Q}}\). Then [cf. I. Schur, Sitzungsber. Akad. Wiss. Berlin 1930, 443–449 (1930; JFM 56.0110.02)] the Galois group of \(f_ n(X)\) is the alternating group \(A_ n\) if 4 divides \(n\) and it is equal to the symmetric group \(S_ n\) otherwise.
This paper gives a new elegant proof of this fact making efficient use of \(p\)-adic Newton polygons to find out things about the degrees of the factors of \(f_ n(X)\) over the \(p\)-adic completions \({\mathbb Q}_ p\).

Reviewer: M. Hazewinkel (Amsterdam)

MSC:

11R32	Galois theory
12F10	Separable extensions, Galois theory

Keywords:

Galois groups of the exponential Taylor polynomials; p-adic Newton polygons

Citations:

JFM 56.0110.02