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A046655
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Numbers whose sum of the squares of divisors is also a square number.
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6
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1, 42, 246, 287, 728, 1434, 1673, 1880, 4264, 6237, 9799, 9855, 18330, 21352, 21385, 24856, 36531, 39990, 46655, 57270, 66815, 92664, 125255, 156570, 182665, 208182, 212949, 242879, 273265, 380511, 391345, 411558, 539560, 627215, 693160, 730145, 741096
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OFFSET
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1,2
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REFERENCES
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Jean-Marie De Koninck, Ces nombres qui nous fascinent, Entry 42, p. 16, Ellipses, Paris, 2008.
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LINKS
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EXAMPLE
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a(3) = 246 = 2*3*41 with 8 divisors: 1, 2, 3, 6, 41, 82, 123, 246. The sum of squares of the divisors is 84100 = 290^2, also a square.
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MATHEMATICA
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Select[Range[750000], IntegerQ[Sqrt[DivisorSigma[2, #]]] &] (* Jayanta Basu, Jun 27 2013 *)
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PROG
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(PARI) for( n=1, 10^6, issquare(sigma(n, 2)) && print1(n", ")) \\ M. F. Hasler, Oct 05 2008
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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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