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Search: id:A135243
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| A135243 |
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Numbers n such that sigma(n)=6*(reversal(n)-n). |
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+0
2
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| 34, 394, 3994, 39994, 2309882, 3070463, 7796129, 205207782, 225073882, 478854106, 644154038, 1556396391, 3154222593, 3165974493, 5951924107, 10444787521, 12114130241, 20611191282, 58403366517, 71103822309
(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=4*10^m-6 is a semiprime (and 2*10^m-3 is prime) 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(34)=54=6*(43-34)=6*(reversal(34)-34), so 34 is in the sequence.
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MATHEMATICA
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Do[If[6(FromDigits@Reverse@IntegerDigits@n-n)==DivisorSigma[1, n], Print[n]], {n, 70000000}]
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CROSSREFS
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Cf. A135242.
Sequence in context: A101092 A034978 A059338 this_sequence A033914 A159655 A107917
Adjacent sequences: A135240 A135241 A135242 this_sequence A135244 A135245 A135246
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KEYWORD
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base,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(8)-a(20) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Dec 21 2008
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