Cohen's classification conjecture for sums of a 5-potent and an n-potent

Let Fq\mathbb{F}_q be a finite field of order q=pvq=p^v, where pp is prime and vv is a positive integer. For an integer r>1r>1, call aFqa\in\mathbb{F}_q rr-potent if ar=aa^r=a, and let CrC_r denote the set of all rr-potents. Under the normal conditions, every element of Fq\mathbb{F}_q is a sum of a 5-potent and an nn-potent only for the pairs

(q,n){(3,2),(5,2),(5,3),(7,4),(9,3),(9,5),(13,5),(13,7),(17,9),(25,9),(25,13),(29,15),(41,21),(49,25),(53,27),(73,37),(81,41),(125,63)}.(q,n)\in\{(3,2),(5,2),(5,3),(7,4),(9,3),(9,5),(13,5),(13,7),(17,9),(25,9),(25,13),(29,15),(41,21),(49,25),(53,27),(73,37),(81,41),(125,63)\}.

Here the normal conditions are those imposed in the paper for the finite-field problem, including n>1n>1 and the reduction to exponents compatible with q1q-1. This conjecture proposes a complete classification of finite fields satisfying the stated sum condition; the paper says that its results confirm the conjecture for all finite fields satisfying the condition.

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Primary source

Juncheng Zhou, Peter V. Danchev and Hongfeng Wu, “Finite fields whose members are the sum of a potent and a 5-potent”, arXiv:2512.16942 (2026).

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