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A020486
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Average of squares of divisors is an integer: sigma_0(n) divides sigma_2(n).
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15
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1, 3, 4, 5, 7, 11, 12, 13, 15, 17, 19, 20, 21, 23, 25, 27, 28, 29, 31, 33, 35, 37, 39, 41, 43, 44, 47, 48, 49, 51, 52, 53, 55, 57, 59, 60, 61, 65, 67, 68, 69, 71, 73, 75, 76, 77, 79, 83, 84, 85, 87, 89, 91, 92, 93, 95, 97, 100, 101, 103, 105, 107, 108, 109, 111, 112, 113, 115, 116
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[150], Divisible[DivisorSigma[2, #], DivisorSigma[0, #]]&] (* Harvey P. Dale, May 03 2011 *)
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PROG
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(Haskell)
a020486 n = a020486_list !! (n-1)
a020486_list = filter (\x -> a001157 x `mod` a000005 x == 0) [1..]
(Magma) [n: n in [1..120] | IsZero(DivisorSigma(2, n) mod NumberOfDivisors(n))]; // Bruno Berselli, Apr 11 2013
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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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