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Waring's Problem Solved for Integers with Two Distinct Digits in Base b


Core Concepts
Every sufficiently large integer can be expressed as the sum of a limited number of k-th powers of integers with only two distinct digits in their base b representation.
Abstract

This research paper presents a solution to a variant of Waring's problem, a classical problem in additive number theory. Waring's problem asks whether, for every integer k ≥ 2, there exists an integer s such that every sufficiently large integer can be written as the sum of at most s k-th powers of natural numbers. This paper addresses a specific case of Waring's problem where the integers used to generate the k-th powers are restricted to those having only two distinct digits in their base b representation.

Bibliographic Information:

Green, B. (2024). Waring’s problem with restricted digits. arXiv:2309.09383v3 [math.NT].

Research Objective:

The paper investigates whether a modified version of Waring's problem holds true when the integers used to generate the k-th powers are limited to those with only two distinct digits in their base b representation.

Methodology:

The research employs the Hardy-Littlewood circle method, a powerful technique in analytic number theory, to analyze the problem. The author introduces a novel "log-free Weyl-type estimate" for k-th powers with restricted digits, which plays a crucial role in the proof. The argument also involves decoupling techniques, additive combinatorics, and analysis of digital expansions.

Key Findings:

The paper proves that for any integers k ≥ 2 and b ≥ 3, and for any two distinct coprime digits d1 and d2 in base b, every sufficiently large integer can be represented as the sum of a limited number of k-th powers of integers whose base b representation contains only the digits d1 and d2. The paper provides an upper bound for the number of k-th powers required, which is a function of b and k.

Main Conclusions:

The study successfully demonstrates that integers with restricted digits in a given base can still form an asymptotic basis for Waring's problem. This finding significantly expands the known cases where Waring's problem holds true and provides new insights into the additive properties of integers with specific digital restrictions.

Significance:

This research contributes significantly to additive number theory by solving a variant of Waring's problem with a novel approach. The introduction of the "log-free Weyl-type estimate" and the application of decoupling techniques offer new tools and perspectives for tackling similar problems in number theory and related fields.

Limitations and Future Research:

While the paper provides an upper bound for the number of k-th powers required, the constant factor in the bound might be further optimized. Additionally, exploring the problem with more than two allowed digits or with different digit restrictions could lead to new interesting results and generalizations.

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Stats
The paper considers bases b ≥ 3. The set of integers considered includes all non-negative integers whose digits in base b are either d1 or d2, where d1 and d2 are distinct and coprime digits in base b. The paper proves that every sufficiently large integer can be represented as the sum of at most b^160k^2 k-th powers of integers from the defined set.
Quotes
"One of the most celebrated results in additive number theory is Hilbert’s theorem that the kth powers are an asymptotic basis of finite order." "Our main result in this paper is that a statement of this type holds when S is the set of integers whose base b expansion contains just two different (fixed) digits."

Key Insights Distilled From

by Ben Green at arxiv.org 11-19-2024

https://arxiv.org/pdf/2309.09383.pdf
Waring's problem with restricted digits

Deeper Inquiries

Can the techniques used in this paper be extended to solve Waring's problem for integers with more than two distinct digits in their base b representation?

It is plausible that the techniques in the paper could be extended to handle integers with more than two distinct digits, but this would likely introduce significant technical challenges. Here's why: Decoupling: The decoupling argument in Section 5 relies on splitting the digits into disjoint subsets and then applying Cauchy-Schwarz to isolate the influence of each subset. With more digits, the number of terms in the decoupled expression grows, potentially making it harder to control the resulting bounds. Additive Expansion: Theorem 2.3, used for additive expansion in Section 6, specifically deals with subsets of {0,1}n. Generalizing this to handle more digits would require a different approach or a suitable extension of this theorem. Digital to Diophantine: Proposition 2.4 in Section 7 connects the number of non-zero digits to additive energy. This connection might become more intricate with a larger digit set, potentially requiring a more sophisticated analysis of the additive structure. Therefore, while a direct extension might not be straightforward, adapting the core ideas of decoupling, additive expansion, and the link between digital representations and additive properties could potentially provide a path forward. However, new insights and technical tools would likely be needed to overcome the added complexity.

What are the computational implications of this result for problems related to integer factorization or cryptography?

The results in this paper are primarily theoretical and don't directly translate into practical algorithms for integer factorization or cryptographic applications. Here's why: Non-Constructive Bounds: The proof of Theorem 1.1 establishes the existence of a bound on the number of k-th powers needed, but it doesn't provide an efficient method to find these powers. The use of tools like the pigeonhole principle and Dirichlet's theorem in the proof often leads to non-constructive arguments. Large Constants: The bound obtained in Theorem 1.1 involves large constants (b160k²), making it impractical for computational purposes. Even if the proof were made constructive, the sheer size of the numbers involved would make any resulting algorithm infeasible. Specialized Digit Sets: The result focuses on integers with a very specific digital structure (only two distinct digits in base b). This specialization limits its applicability to problems like factorization, where the integers involved don't usually exhibit such restrictions. While this work doesn't have direct computational implications for factorization or cryptography, it advances our theoretical understanding of additive number theory. Such theoretical progress can sometimes lay the groundwork for future breakthroughs, but as of now, this result doesn't pose any immediate threats or offer practical tools for these computationally challenging problems.

If we consider the set of all possible universes governed by different mathematical laws, would there be a universe where Waring's problem has a different solution or remains unsolved?

This question delves into the philosophy of mathematics and the nature of mathematical truth. There are different schools of thought on this: Mathematical Platonism: This view holds that mathematical objects and truths exist independently of our minds and the physical universe. In this framework, Waring's problem has a definite answer, true in all possible universes, regardless of their specific physical laws or mathematical structures. Mathematical Formalism: Formalists view mathematics as a game of symbols and rules. From this perspective, the "truth" of a mathematical statement depends on the chosen axioms and rules of inference. It's conceivable that different universes could be modeled by different axiomatic systems, potentially leading to different outcomes for Waring's problem. Mathematical Constructivism: Constructivists emphasize the role of explicit constructions in mathematics. For them, a statement is true only if it can be proven constructively. In a universe with different computational principles, the notion of a "constructive proof" might differ, potentially affecting the solvability of Waring's problem. Therefore, whether Waring's problem has a universally consistent answer or could vary across different hypothetical universes depends on one's philosophical stance on the nature of mathematics. It's a fascinating question that bridges mathematics, philosophy, and the nature of reality itself.
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