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Search: id:A135242
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| A135242 |
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Numbers n such that sigma(n)=2*(n-reversal(n)). |
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+0
2
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| 10, 51, 430, 591, 922, 5991, 8350, 20210, 28810, 59211, 59991, 6673581, 8179030, 20158910, 203887910, 833549650, 2263048910, 2814442310, 7823347543, 78551146723, 81896108650
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If n=6*10^m-9 is semiprime then n is in the sequence (the proof is easy). Next term is greater than 7*10^7.
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EXAMPLE
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sigma(51)=72=2*(51-15)=2*(51-reversal(51)), so 51 is in the sequence.
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MATHEMATICA
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Do[If[2(n-FromDigits@Reverse@IntegerDigits@n)==DivisorSigma[1, n], Print[n]], {n, 70000000}]
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CROSSREFS
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Cf. A135243.
Sequence in context: A077044 A069038 A030183 this_sequence A041186 A058827 A028994
Adjacent sequences: A135239 A135240 A135241 this_sequence A135243 A135244 A135245
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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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EXTENSIONS
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a(15)-a(21) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Dec 21 2008
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