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Search: id:A066764
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| A066764 |
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Numbers n such that (n, sigma(n)) lies on a circle with integral radius centered at the origin, i.e. n^2 + sigma(n)^2 is a square. |
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+0
1
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| 3, 8, 30, 140, 315, 319, 460, 840, 864, 936, 1040, 1287, 1836, 2480, 2600, 6076, 6200, 7788, 11398, 12035, 12415, 12584, 13260, 13734, 15886, 18480, 26078, 33820, 40640, 42665, 46200, 55860, 68352, 70266, 70645, 75330, 78939, 81740, 98230
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OFFSET
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1,1
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EXAMPLE
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3^2 + sigma(3)^2 = 9 + 16 = 5^2; so 3 is a term of the sequence.
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MATHEMATICA
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Select[ Range[ 1, 10^5 ], IntegerQ[ Sqrt[ #^2 + DivisorSigma[ 1, # ]^2 ] ] & ]
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CROSSREFS
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Adjacent sequences: A066761 A066762 A066763 this_sequence A066765 A066766 A066767
Sequence in context: A096161 A074501 A009123 this_sequence A059171 A078619 A066304
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KEYWORD
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nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 17 2002
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