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A146746
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Numbers n such that sigma_1(n+1)*sigma_1(n)/(sigma_1(n+1)+sigma_1(n))=c, c an integer.
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0
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5, 14, 54, 55, 56, 58, 70, 87, 88, 89, 114, 118, 123, 125, 178, 201, 204, 206, 220, 246, 354, 358, 417, 419, 459, 478, 500, 534, 549, 594, 604, 620, 646, 654, 663, 715, 718, 753, 834, 835, 838, 894, 957
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| A000203(n+1)*A000203(n)/(A000203(n+1)+A000203(n)) = c, c an integer.
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MATHEMATICA
| sQ[n_]:=Module[{sn=DivisorSigma[1, n], sn1=DivisorSigma[1, n+1]}, Divisible[sn sn1, sn+sn1]]; Select[Range[1000], sQ] (* From Harvey P. Dale, Apr 21 2011 *)
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CROSSREFS
| Cf. A083795, A063647, A000203
Sequence in context: A197601 A133751 A005504 * A073541 A055488 A177049
Adjacent sequences: A146743 A146744 A146745 * A146747 A146748 A146749
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KEYWORD
| easy,nonn
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AUTHOR
| Ctibor O. Zizka (c.zizka(AT)email.cz), Nov 01 2008
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EXTENSIONS
| Corrected by Harvey P. Dale, Apr 21 2011.
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