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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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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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LINKS
| Harry J. Smith, Table of n, a(n) for n=1,...,731
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EXAMPLE
| 3^2 + sigma(3)^2 = 9 + 16 = 5^2; so 3 is a term of the sequence.
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MATHEMATICA
| Select[ Range[ 1, 10^5 ], IntegerQ[ Sqrt[ #^2 + DivisorSigma[ 1, # ]^2 ] ] & ]
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PROG
| (PARI) { n=0; for (m=1, 10^10, if (issquare(m^2 + sigma(m)^2), write("b066764.txt", n++, " ", m); if (n==1000, return)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Mar 24 2010]
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CROSSREFS
| Sequence in context: A161779 A074501 A009123 * A059171 A078619 A066304
Adjacent sequences: A066761 A066762 A066763 * A066765 A066766 A066767
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KEYWORD
| nonn
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AUTHOR
| Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Jan 17 2002
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