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A073082
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Numbers n such that sum k/d(k) is an integer, where d(k) is the k-th divisor of n (the divisors of n are in increasing order).
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1
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1, 2, 9, 10, 39, 348, 1272, 10682, 18275, 414912, 5606336, 8712340, 20920564, 47201552, 140142814, 240574848, 5459371212, 16993264107, 22955387784, 23807694876, 33482496720
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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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EXAMPLE
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Divisors of 39 are [1, 3, 13, 39] and 1/1 + 2/3 + 3/13 + 4/39 = 2 is an integer hence 39 is in the sequence.
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MAPLE
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with(numtheory): a:=proc(n) local div: div:=divisors(n): if type(sum(k/div[k], k=1..tau(n)), integer)=true then n else fi end: seq(a(n), n=1..50000); # Emeric Deutsch, Aug 04 2005
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MATHEMATICA
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Do[d = Divisors[n]; If[IntegerQ[Dot[Range[Length[d]], Map[(1/#)&, d]]], Print[n]], {n, 1, 10^8}] (* Ryan Propper, Jul 30 2005 *)
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PROG
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(PARI) /* to have b(n)=sum k/d(k) */ b(n)=sum(i=1, numdiv(n), i/component(divisors(n), i))
(PARI) isok(n) = my(d=divisors(n)); denominator(sum(k=1, #d, k/d[k])) == 1; \\ Michel Marcus, Sep 10 2017
(Magma) [k:k in [1..500000]|IsIntegral( &+[m/Divisors(k)[m]:m in [1..#Divisors(k)]])]; // Marius A. Burtea, Dec 06 2019
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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Two further terms from Lambert Klasen (lambert.klasen(AT)gmx.net), Oct 31 2005
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STATUS
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approved
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