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A115749
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Numbers n such that sigma(n)=8*reversal(n).
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0
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OFFSET
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1,1
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COMMENTS
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If p=3*10^n+17 is prime then 3*p is in the sequence because sigma(3*p)=4*(3*10^n+18)=12*10^n+72=8*(15*10^(n-1)+9)=8* reversal(9*10^n+51)=8*reversal(3*p). Also if p=(2*10^n+1)/3 is prime then 123*p is in the sequence (the proof is easy). Next term is greater than 13*10^7.
a(11) > 10^12. - Giovanni Resta, Oct 28 2012
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LINKS
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Table of n, a(n) for n=1..10.
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EXAMPLE
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82000041 is in the sequence because sigma(82000041)
=112000224=8*14000028=8*reversal(82000041).
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MATHEMATICA
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Do[If[DivisorSigma[1, n]==8*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 130000000}]
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CROSSREFS
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Cf. A069216, A105324, A114928, A115747, A115748.
Sequence in context: A278156 A249461 A292626 * A105323 A206756 A203272
Adjacent sequences: A115746 A115747 A115748 * A115750 A115751 A115752
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KEYWORD
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base,more,nonn
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AUTHOR
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Farideh Firoozbakht, Feb 12 2006
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EXTENSIONS
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a(9)-a(10) from Donovan Johnson, Dec 21 2008
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STATUS
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approved
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