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Search: id:A097648
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| A097648 |
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a(n) is the least non-palindromic number m such that phi(m)=phi(reversal(m))=4*10^(n+2), or 0 if no such number exists. |
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+0
2
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| 10040, 110440, 1014040, 11154440, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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This sequence is a subsequence of A097647. It seems that 10 divides all terms of this sequence. Conjecture: This sequence is infinite.
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LINKS
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C. Rivera, f(p)=f(p') , puzzle 282
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FORMULA
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a[n_]:=(For[m=4*10^(n+2), !(m!=FromDigits[Reverse[IntegerDigits[m]]] &&EulerPhi[m]==EulerPhi[FromDigits[Reverse[IntegerDigits [m]]]]==4*10^(n+2)), m++ ];m)
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EXAMPLE
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a(4)=11154440 because phi(11154440)=phi(04445111)=4000000 and 11154440 is the earliest non-palindromic number with this property.
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MATHEMATICA
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a[n_]:=(For[m=4*10^(n+2), !(m!=FromDigits[Reverse[IntegerDigits[m]]] &&EulerPhi[m]==EulerPhi[FromDigits[Reverse[IntegerDigits [m]]]]==4*10^(n+2)), m++ ]; m); Do[Print[a[n]], {n, 4}]
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CROSSREFS
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Cf. A097647.
Adjacent sequences: A097645 A097646 A097647 this_sequence A097649 A097650 A097651
Sequence in context: A096211 A052095 A033533 this_sequence A023356 A083965 A043641
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KEYWORD
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more,nonn
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AUTHOR
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Farideh Firoozbakht (f.firoozbakht(AT)math.ui.ac.ir), Sep 04 2004
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EXTENSIONS
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Better definition and more terms from David Wasserman (dwasserm(AT)earthlink.net), Dec 28 2007
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