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Search: id:A087998
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| A087998 |
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a(n)=Min{x; sigma[x]=2x+2n}. |
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+0
4
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| 6, 20, 12, 8925, 56, 40, 24, 272, 550, 208, 176, 1312, 112, 80, 48, 945, 572, 928, 2205, 5696, 736, 9555, 350, 490, 60, 416, 352, 90, 84, 160, 96, 24704, 108, 3904, 260, 487936, 132, 1575, 340, 234, 156, 22144, 2752, 2624, 460, 306, 500, 475678, 204
(list; graph; listen)
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OFFSET
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0,1
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COMMENT
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The satellite problem: sigma[x]=2x+odd seems much more difficult. Solutions[square or 2.square! ] I got only for 3,7,17,19,31,39,41,51,59,65,71, 89,115,119,127,161,185,199.
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EXAMPLE
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n=67: 2n=134, first solution to sigma[x]=2x+134
is a(67)=1958912;
n=0: solution is the least perfect number, a(0)=6;
2n=12, 2n=56 provide large number of solutions.
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MATHEMATICA
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ds[x_, de_] := DivisorSigma[1, x]-2*x-de a[n_] := Block[{m=1, s=ds[m, n]}, While[(s !=0)&& !Greater[m, 10000000], m++ ]; m]; Table[a[n], {n, 1, 100}]//Timing
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CROSSREFS
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Sequence in context: A075251 A090590 A002566 this_sequence A096823 A007253 A096897
Adjacent sequences: A087995 A087996 A087997 this_sequence A087999 A088000 A088001
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Oct 13 2003
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