What should be assumed about the integral polynomials $f₁\left(x\right),...,f_k\left(x\right)$ in order that the solvability of the congruence $f₁\left(x\right)f₂\left(x\right)\cdots f_k\left(x\right)\equiv 0\left(modp\right)$ for sufficiently large primes p implies the solvability of the equation $f₁\left(x\right)f₂\left(x\right)\cdots f_k\left(x\right)=0$ in integers x? We provide some explicit characterizations for the cases when $f_j\left(x\right)$ are binomials or have cyclic splitting fields.

We prove that almost all positive even integers $n$ can be represented as $p_2^2+p_3^3+p_4^4+p_5^5$ with $|p_k^k-\frac{1}{4}N|\le N^{1-1/54+\epsilon }$ for $2\le k\le 5$. As a consequence, we show that each sufficiently large odd integer $N$ can be written as $p_1+p_2^2+p_3^3+p_4^4+p_5^5$ with $|p_k^k-\frac{1}{5}N|\le N^{1-1/54+\epsilon }$ for $1\le k\le 5$.

Let $q$ be a complex number, $m$ be a positive rational integer and $l_m\left(q\right)=inf\{\left|P\left(q\right)\right|,P\in {\mathbb{Z}}_m\left[X\right],P\left(q\right)\ne 0\}$, where ${\mathbb{Z}}_m\left[X\right]$ denotes the set of polynomials with rational integer coefficients of absolute value $\le m$. We determine in this note the maximum of the quantities $l_m\left(q\right)$ when $q$ runs through the interval $]m,m+1[$. We also show that if $q$ is a non-real number of modulus $\>1$, then $q$ is a complex Pisot number if and only if $l_m\left(q\right)\>0$ for all $m$.