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A066784 Numbers n such that (n, sigma(n)) lies on the hyperbola y^2 - x^2 = m^2, for some natural number m, i.e., sigma(n)^2 - n^2 = m^2. 0
1, 90, 392448, 411264, 804384, 871416 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..6.

EXAMPLE

sigma(90)^2 - 90^2 = 234^2 - 90^2 = 216^2, so 90 is a term of the sequence.

MATHEMATICA

Select[ Range[ 1, 10^6 ], IntegerQ[ Sqrt[ DivisorSigma[ 1, # ]^2 - #^2 ] ] & ]

CROSSREFS

Sequence in context: A172572 A052277 A172671 * A135321 A135428 A028672

Adjacent sequences:  A066781 A066782 A066783 * A066785 A066786 A066787

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Jan 18 2002

STATUS

approved

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Last modified March 23 11:10 EDT 2019. Contains 321424 sequences. (Running on oeis4.)