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

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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 a∈Fqa\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 q−1q-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.

References

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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