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Search: id:A114928
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| A114928 |
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Numbers n such that sigma(n)=4*reversal(n). |
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4
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OFFSET
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1,1
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COMMENT
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If p=(2*10^n+1)/3 is prime then m=6*p is in the sequence because sigma(m)=sigma(6*p)=12*(2*10^n+4)/3=4*(2*10^n+4)=4* reversal(4*10^n+2)=4*reversal(6*(2*10^n+1)/3)=4*reversal(6*p) =4*reversal(m). Next term is greater than 5*10^8.
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EXAMPLE
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492 is in the sequence because sigma(492)=sigma(4*3*41)=7*4*42
=4*294=4*reversal(492).
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MATHEMATICA
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Do[If[DivisorSigma[1, n]==4*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 500000000}]
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CROSSREFS
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Cf. A069216, A105324, A114927.
Sequence in context: A105919 A091082 A064302 this_sequence A127545 A027318 A090297
Adjacent sequences: A114925 A114926 A114927 this_sequence A114929 A114930 A114931
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KEYWORD
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base,more,nonn
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AUTHOR
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Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 28 2006
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