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A125775
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Numbers k such that 5^k mod k = 5^k mod k^2.
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5
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1, 2, 4, 5, 6, 12, 25, 42, 52, 84, 125, 156, 186, 372, 625, 1092, 1218, 1302, 1806, 2436, 2604, 2756, 3125, 3612, 4836, 5334, 7212, 8268, 10668, 12324, 15625, 15918, 18858, 19140, 20771, 24492, 26080, 31668, 31836, 33852, 37716, 37758, 40487, 41542
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OFFSET
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1,2
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COMMENTS
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Includes all powers of 5 (A000351).
a(2) = 2, a(4) = 5, a(35) = 20771 and a(43) = 40487 are the only listed primes. More known primes are listed in A123692.
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LINKS
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MATHEMATICA
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Do[f=PowerMod[5, n, n]; g=PowerMod[5, n, n^2]; If[f==g, Print[n]], {n, 1, 1000000}]
Select[Range[42000], PowerMod[5, #, #]==PowerMod[5, #, #^2]&] (* Harvey P. Dale, Aug 20 2022 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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