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A165701
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Numbers n such that 5^n-6 is prime.
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3
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2, 4, 5, 6, 10, 53, 76, 82, 88, 242, 247, 473, 586, 966, 1015, 1297, 1825, 2413, 2599, 2833, 5850, 5965, 6052, 27199, 49704, 79000
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OFFSET
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1,1
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COMMENTS
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Numbers corresponding to the a(n) for n>11 are probable prime.
If Q is a 4-perfect number and gcd(Q, 5*(5^a(n)-6))=1 then m=5^(a(n)-1)
(5^a(n)-6)*Q is a solution of the equation sigma(x)=5(x+Q)(see comment lines of the sequence A058959). 142990848 is the smallest 4-perfect number m such that 5 doesn't divide m.
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LINKS
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MATHEMATICA
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Do[If[PrimeQ[5^n-6], Print[n]], {n, 8888}]
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PROG
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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