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A239668
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Sum of the composite divisors of n^2.
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1
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0, 4, 9, 28, 25, 85, 49, 124, 117, 209, 121, 397, 169, 389, 394, 508, 289, 841, 361, 953, 730, 917, 529, 1645, 775, 1265, 1089, 1757, 841, 2810, 961, 2044, 1714, 2129, 1754, 3745, 1369, 2645, 2362, 3929, 1681, 5174, 1849, 4109, 3742, 3845, 2209, 6637, 2793, 5459, 3970
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = sigma(n^2) - sopf(n^2) - 1.
a(n) = n^2 if n is prime. - Zak Seidov, Mar 31 2014
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EXAMPLE
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For n=2, the sum of the composite factors of n^2 is equal to 4.
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MAPLE
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A008472 := n -> add(d, d = select(isprime, numtheory[divisors](n))):
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MATHEMATICA
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a[n_] := DivisorSum[n^2, If[# == 1 || PrimeQ[#], 0, #]& ]; Array[a, 60] (* Jean-François Alcover, Dec 18 2015 *)
Table[Total[Select[Divisors[n^2], CompositeQ]], {n, 60}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 06 2017 *)
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PROG
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(PARI) a(n) = sumdiv(n^2, d, d*(!isprime(d) && (d != 1))); \\ Michel Marcus, Mar 31 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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