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Search: id:A114930
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| A114930 |
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Numbers n such that phi(n)=2*reversal(n). |
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+0
2
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OFFSET
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1,1
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COMMENT
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If m>1 and p=3*10^m+7 is prime then 90*p is in the sequence because phi(90*p)=phi(90)*phi(p)=24*(3*10^m+6)=2*(36*10^m+72) =2*reversal(27*10^m+63)=2*reversal(9*p)=2*reversal(90*p). Note that 30 divides all known terms of this sequence. Next term is greater than 11*10^7.
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EXAMPLE
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637062480 is in the sequence because phi(637062480)=2*84260736=
2*reversal(637062480).
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MATHEMATICA
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Do[If[EulerPhi[n]==2*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 110000000}]
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CROSSREFS
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Cf. A069215, A114931.
Sequence in context: A007992 A033288 A057880 this_sequence A068757 A031836 A094494
Adjacent sequences: A114927 A114928 A114929 this_sequence A114931 A114932 A114933
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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 29 2006
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