On logarithmically Benford Sequences

• Published in: Proceedings of the American Mathematical Society 2016-11, Vol.144 (11), p.4599-4608
• Main Authors: Chen, Evan, Park, Peter S., Swaminathan, Ashvin A.
• Format: Article
• Language: English
• Subjects: A. ALGEBRA, NUMBER THEORY, AND COMBINATORICS; Research article
• ISSN: 0002-9939; 1088-6826
• DOI: 10.1090/proc/13112

Let I⊂N\mathcal {I} \subset \mathbb {N} be an infinite subset, and let {ai}i∈I\{a_i\}_{i \in \mathcal {I}} be a sequence of nonzero real numbers indexed by I\mathcal {I} such that there exist positive constants m,C1m, C_1 for which |ai|≤C1⋅im|a_i| \leq C_1 \cdot i^m for all i∈Ii \in \mathcal {I}. Furthermore, let ci∈[−1,1]c_i \in [-1,1] be defined by ci=aiC1⋅imc_i = \frac {a_i}{C_1 \cdot i^m} for each i∈Ii \in \mathcal {I}, and suppose the cic_i’s are equidistributed in [−1,1][-1,1] with respect to a continuous, symmetric probability measure μ\mu. In this paper, we show that if I⊂N\mathcal {I} \subset \mathbb {N} is not too sparse, then the sequence {ai}i∈I\{a_i\}_{i \in \mathcal {I}} fails to obey Benford’s Law with respect to arithmetic density in any sufficiently large base, and in fact in any base when μ([0,t])\mu ([0,t]) is a strictly convex function of t∈(0,1)t \in (0,1). Nonetheless, we also provide conditions on the density of I⊂N\mathcal {I} \subset \mathbb {N} under which the sequence {ai}i∈I\{a_i\}_{i \in \mathcal {I}} satisfies Benford’s Law with respect to logarithmic density in every base. As an application, we apply our general result to study Benford’s Law-type behavior in the leading digits of Frobenius traces of newforms of positive, even weight. Our methods of proof build on the work of Jameson, Thorner, and Ye, who studied the particular case of newforms without complex multiplication.