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A067719
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Numbers k such that sigma(k^2 + 1) == 0 (mod k).
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3
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1, 2, 3, 9, 12, 21, 33, 72, 93, 196, 228, 252, 360, 475, 850, 1458, 1725, 1752, 2100, 2241, 2584, 3007, 3404, 4347, 4743, 5544, 5720, 6555, 6600, 9909, 10512, 14175, 15507, 16680, 19404, 26460, 29008, 29484, 36003, 36400, 37107, 46728, 88209, 88641, 89424, 94770
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OFFSET
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1,2
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LINKS
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MAPLE
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q:= n-> is(irem(numtheory[sigma](n^2+1), n)=0):
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MATHEMATICA
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Select[Range[50000], Divisible[DivisorSigma[1, #^2+1], #]&] (* Harvey P. Dale, Nov 04 2011 *)
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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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