Davenport constants with growing binary rank

Abstract

We study the correction to the standard lower bound $D^*$ for Davenport constants of finite abelian groups with a growing elementary two-component. For every fixed nontrivial abelian $p$-group $H$ of odd order, we prove $D(H\oplus C_2^r)=D^*(H\oplus C_2^r)+(D(H)-1)\log_2 r+O_H(1)$, with a uniform version for varying $H$. For $C_3\oplus C_2^r$, we determine exact values on explicit infinite intervals of ranks. More generally, the correction is logarithmic or smaller precisely when the fixed group has at most one odd prime divisor. We show that the two-primary part affects the logarithmic coefficient: for $C_{24}\oplus C_2^r$, the ratio $(D-D^*)/\log_2 r$ has limsup at least $2.4933231\ldots>2$, whereas for $C_3\oplus C_2^r$ the limit is $2$. These upper limiting coefficients are unbounded even with the odd prime fixed. The proofs use binary codes and finite-field Fourier analysis.