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A186429
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Numbers n such that sum_{i=1..n} d(i)^2 is a square c^2, where d(i) is the number of divisors of i.
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1
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1, 3, 28, 85, 151, 302, 864, 3197, 4780, 5438, 5815, 6413, 7769, 7985, 11062, 16672, 24805, 27379, 35435, 41718, 45047, 58383, 69835, 70235, 76305, 91178, 95963, 97763, 103173, 111375, 118498, 138405, 158200, 170333, 184132, 191707, 201693
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OFFSET
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1,2
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COMMENTS
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c is from (1,3,21,49,74,121,249,590,765,...)
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LINKS
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EXAMPLE
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For n=3 we have (1*1+2*2+2*2)= 3*3 so n=3 belongs to the sequence.
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MATHEMATICA
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Position[Accumulate[DivisorSigma[0, Range[210000]]^2], _?(IntegerQ[ Sqrt[ #]]&)]//Flatten (* Harvey P. Dale, Jul 17 2016 *)
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PROG
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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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