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Search: id:A130001
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| A130001 |
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Numbers n such that phi(n) is the arithmetic mean of n and reversal(n). |
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+0
2
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OFFSET
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1,2
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COMMENT
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A number of the form 3*(32*10^n-29) is in the sequence iff n>1 and 1/3*(32*10^n-29) is prime (the proof is easy). The first three such terms are 3*(32*10^3-29),3*(32*10^4-29)& 3*(32*10^9-29). There is no further term up to 2*10^9.
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EXAMPLE
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phi(950039541)=1/2*(950039541+145930059) so 950039541 is in the sequence.
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MATHEMATICA
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r[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; Do[c=r[n]; If[c+n== 2EulerPhi[n], Print[n]], {n, 200000000}]
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CROSSREFS
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Cf. A130000, A130002, A130013, A130031.
Sequence in context: A128389 A114660 A078518 this_sequence A116228 A116253 A116265
Adjacent sequences: A129998 A129999 A130000 this_sequence A130002 A130003 A130004
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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), Apr 29 2007
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