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A259185
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Numbers n such that 1 - sigma(n) + sigma(n)^2 is prime.
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3
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2, 3, 4, 5, 8, 9, 10, 12, 17, 18, 20, 24, 26, 30, 32, 36, 38, 40, 41, 45, 46, 51, 54, 55, 56, 58, 59, 60, 66, 70, 71, 72, 78, 86, 87, 89, 91, 92, 94, 95, 99, 101, 102, 104, 106, 108, 110, 115, 116, 119, 123, 125, 131, 134, 138, 142, 143, 144, 154, 159, 164
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OFFSET
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1,1
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LINKS
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MAPLE
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MATHEMATICA
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Select[ Range[10000], PrimeQ[ 1 - DivisorSigma[1, n] + DivisorSigma[1, n]^2] & ]
Select[ Range[10000], PrimeQ[ Cyclotomic[6, DivisorSigma[1, #]]] &]
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PROG
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(Magma) [n: n in [1..180] | IsPrime(1 - SumOfDivisors(n) + SumOfDivisors(n)^2)]; // Vincenzo Librandi, Nov 20 2015
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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