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Search: id:A066244
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| A066244 |
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Numbers n such that sigma(n+2)-2sigma(n+1)+sigma(n) = n. |
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+0
1
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OFFSET
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1,1
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COMMENT
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The equation here is the difference equation (applied to sigma) corresponding to the differential equation y" = x (Hooke's law with constant = -1).
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EXAMPLE
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sigma(40)-2*sigma(39)+sigma(38) = 90 - 2*56 + 60 = 38, so 38 is a term of the sequence.
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MATHEMATICA
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Select[Range[1, 10^6], DivisorSigma[1, # + 2] - 2*DivisorSigma[1, # + 1] + DivisorSigma[1, # ] == # &]
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CROSSREFS
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Sequence in context: A098772 A075796 A132396 this_sequence A055689 A028442 A062982
Adjacent sequences: A066241 A066242 A066243 this_sequence A066245 A066246 A066247
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KEYWORD
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more,nonn
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AUTHOR
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Joseph L. Pe (joseph_l_pe(AT)hotmail.com), Dec 19 2001
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EXTENSIONS
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a(5) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Feb 01 2009
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