2020/96/3-4 (8)
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DOI: 10.5486/PMD.2020.8683
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pp. 401-422
Strong arithmetic property of certain Stern polynomials
Abstract:
Let $B_{n}(t)$ be the $n$-th Stern polynomial, i.e., the $n$-th term of the sequence defined recursively as $B_{0}(t)=0$, $B_{1}(t)=1$ and $B_{2n}(t)=tB_{n}(t)$, $B_{2n+1}(t)=B_{n}(t)+B_{n-1}(t)$ for $n\in\mathbb{N}$. It is well known that the $i$-th coefficient in the polynomial $B_{n}(t)$ counts the number of hyperbinary representations of $n-1$ containing exactly $i$ digits $1$. In this note, we investigate the existence of odd solutions of the congruence
$$
B_{n}(t)\equiv 1+rt\frac{t^{e(n)}-1}{t-1}\pmod{m},
$$
where $m\in\mathbb{N}_{\geq 2}$ and $r\in\{0,\ldots,m-1\}$ are fixed and $e(n)=\operatorname{deg}B_{n}(t)$. We prove that for $m=2$ and $r\in\{0,1\}$ and for $m=3$ and $r=0$, there are infinitely many odd numbers $n$ satisfying the above congruence. We also present results of some numerical computations.
Keywords: the Stern sequence, the Stern polynomials, congruences, numerical computations
Mathematics Subject Classification: 11P81, 11P83
