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Nov 1, 2023 at 12:10 vote accept Raj Pratap Singh
Nov 1, 2023 at 12:10 vote accept Raj Pratap Singh
Nov 1, 2023 at 12:10
Nov 1, 2023 at 9:34 history edited Fedor Petrov CC BY-SA 4.0
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Nov 1, 2023 at 0:31 history edited Fedor Petrov CC BY-SA 4.0
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Oct 31, 2023 at 20:16 comment added GH from MO The counterexamples to the original conjecture are precisely the Carmichael numbers (and they have at least 3 prime factors).
Oct 31, 2023 at 19:15 comment added GH from MO @SalvoTringali Yes, I figured this out while preparing my dinner. See my comment before yours.
Oct 31, 2023 at 19:15 comment added Salvo Tringali @GHfromMO For a reference, see e.g. Problem 8.2.12 in the 7th edition of Burton's Elementary Number Theory (it's a standard exercise on primitive roots).
Oct 31, 2023 at 19:14 comment added GH from MO I see, if $p-1$ does not divide $k$, then picking a primitive root $g\bmod p$, we have $g^k\not\equiv 1\pmod{p}$, while the sum multiplied by $g^k$ is congruent to itself mod $p$, whence the sum is in fact divisible by $p$.
Oct 31, 2023 at 19:09 comment added GH from MO Can you give a reference for the first sentence?
Oct 31, 2023 at 19:02 history answered Fedor Petrov CC BY-SA 4.0