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Search: id:A112645
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| A112645 |
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Solutions to Abs[sigma[x+1]-sigma[x]]=2. Divisor sums of x and its neighbor x+1 differ from each other either by +2 or by -2. |
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+0
3
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OFFSET
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1,2
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COMMENT
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Observe that form of 8,26,2186 and 1594322 is -1+3^j. Exponents of powers of 3 suitable as number n+1 are as follows: 2,3,7,13,71,103. Is or not the next term 7509466514979724803946715958257546=-1+3^71 ?
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EXAMPLE
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n=1594322=2.797161 while n+1=3^13;
sigma[n]=2391486,sigma[n+1]=2391484
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MATHEMATICA
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ta={{0}}; Do[s=Abs[DivisorSigma[1, n+1]-DivisorSigma[1, n]]; If[Equal[s, 2], ta=Append[ta, n]; Print[n]], {n, 1, 100000000}]; ta=Delete[ta, 1]
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CROSSREFS
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Cf. A000203, A112646, A112647.
Sequence in context: A051669 A027004 A082573 this_sequence A089064 A000810 A129663
Adjacent sequences: A112642 A112643 A112644 this_sequence A112646 A112647 A112648
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KEYWORD
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more,nonn
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AUTHOR
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Labos E. (labos(AT)ana.sote.hu), Sep 28 2005
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