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A114928
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Numbers n such that sigma(n)=4*reversal(n).
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3
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OFFSET
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1,1
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COMMENTS
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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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LINKS
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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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KEYWORD
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base,more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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