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Search: id:A098771
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| A098771 |
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Numbers n such that sigma(n)=sigma(d_1)*sigma(d_2)*...*sigma(d_k) where d_1 d_2 ... d_k is the decimal expansion of n. |
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+0
1
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| 1, 2, 3, 4, 5, 6, 7, 8, 9, 38, 58, 66, 87, 568, 766, 2799, 6478, 6785, 26486, 36685, 36893, 64788, 66758, 67586, 69664, 77686, 276895, 467683, 474668, 488973, 548678, 587667, 658648, 666369, 668954, 839666, 939669, 958968, 968765, 2386698
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Number of terms of this equence up to 15000000 is 72. Has this sequence at least one multi-digit prime term?
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EXAMPLE
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97888745 is in the sequence because sigma(97888745) = 117936000 = sigma(9)*sigma(7)*sigma(8)*sigma(8)*sigma(8)*sigma(7)*sigma(4)*sigma(5).
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MATHEMATICA
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Do[If[h=IntegerDigits[n]; l=Length[h]; !MemberQ[h, 0]&&DivisorSigma[ 1, n]==Product[DivisorSigma[1, h[[k]]], {k, l}], Print[n]] {n, 100000000}]
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CROSSREFS
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Cf. A098684, A098685.
Adjacent sequences: A098768 A098769 A098770 this_sequence A098772 A098773 A098774
Sequence in context: A072482 A064154 A080161 this_sequence A024659 A129513 A024660
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KEYWORD
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base,nonn
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AUTHOR
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Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Oct 03 2004
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