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Search: id:A136542
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| A136542 |
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Numbers n such that sigma(n)=reversal(n)+5. |
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+0
1
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| 57, 58, 597, 1642, 5997, 5998, 51718, 160042, 556438, 599997, 5999998, 15810772, 59999997, 59999998
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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I. If 2*10^m-1 is prime then n=3*(2*10^m-1) is in the sequence(the proof is easy).
II. If 3*10^m-1 is prime then n=2*(3*10^m-1) is in the sequence (the proof is easy).
III. If m>1 and 8*10^m+21 is prime then n=2*(8*10^m+21) is in the sequence(the proof is easy).
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EXAMPLE
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sigma(57)=80=75+5=reversal(57)+5, so 57 is in the sequence.
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MATHEMATICA
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Do[If[DivisorSigma[1, n]==FromDigits@Reverse@IntegerDigits#n+5, Print[n]], {n, 160000000}]
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CROSSREFS
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Cf. A069216.
Sequence in context: A126828 A033377 A036184 this_sequence A042623 A072466 A056082
Adjacent sequences: A136539 A136540 A136541 this_sequence A136543 A136544 A136545
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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 08 2008
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