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Search: id:A136538
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| A136538 |
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Numbers n such that reversal(n)=2*phi(n). |
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+0
1
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| 2, 4, 8, 42, 84, 2763, 4032, 8064, 67314, 86558, 291483, 2700063
(list; graph; listen)
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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 n=9*p is in the sequence (the proof is easy). If n is an even term of the sequence and the largest digit of n is less than 5(3) then 2n is (both numbers 2n & 4n are) in the sequence (the proof is easy). Next term is greater than 10^8.
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EXAMPLE
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Reversal(42)=24=2*12=2*phi(42), so 42 is in the sequence. [Example corrected Jan 25 2008]
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MATHEMATICA
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Do[If[FromDigits@Reverse@IntegerDigits@n==2*EulerPhi[n], Print[n]], {n, 100000000}]
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CROSSREFS
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Cf. A136539.
Sequence in context: A058236 A102918 A018395 this_sequence A018403 A018422 A058816
Adjacent sequences: A136535 A136536 A136537 this_sequence A136539 A136540 A136541
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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 04 2008
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