EN
Let d be a positive integer and α a real algebraic number of degree d + 1. Set $α̲:= (α,α²,...,α^{d})$. It is well-known that
$c(α̲) := lim inf_{q→ ∞} q^{1/d}·||qα̲|| > 0$,
where ||·|| denotes the distance to the nearest integer. Furthermore,
$c(α̲)n^{-1/d} ≤ c(nα̲) ≤ nc(α̲)$
for any integer n ≥ 1. Our main result asserts that there exists a real number C, depending only on α, such that
$c(nα̲) ≤ Cn^{-1/d}$
for any integer n ≥ 1.