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A245787
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Numbers n such that tau(n)*sigma(n) divides n^2.
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1
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1, 26208, 56896, 293760, 997920, 9694080, 23569920, 25159680, 29669760, 67858560, 117849600, 132723360, 208565280, 222963840, 276756480, 427714560, 513786240, 578672640, 628992000, 649503360, 688279680, 714954240, 779950080, 830269440, 979102080, 1037266560
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OFFSET
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1,2
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COMMENTS
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Subsequence of A090777 (numbers n such that sigma(n) divides n^2).
Sequence of numbers k(n) = n^2 / (tau(n) * sigma(n)): 1, 104, 889, 612, 945, 7344, …
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LINKS
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MATHEMATICA
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a245787[n_Integer] := Select[Range[n], Divisible[#^2, DivisorSigma[0, #]*DivisorSigma[1, #]]&] (* Michael De Vlieger, Aug 09 2014 *)
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PROG
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(Magma) [n: n in [1..1000000] | Denominator(n^2 / ((#[d: d in Divisors(n)])* SumOfDivisors(n))) eq 1]
(PARI)
for(n=1, 10^8, if(n^2%(numdiv(n)*sigma(n))==0, print1(n, ", "))) \\ Derek Orr, Aug 08 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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