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Search: id:A115749
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| A115749 |
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Numbers n such that sigma(n)=8*reversal(n). |
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+0
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| 861, 951, 2070, 8241, 900051, 8864151, 9000051, 82000041
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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If p=3*10^n+17 is prime then 3*p is in the sequence because sigma(3*p)=4*(3*10^n+18)=12*10^n+72=8*(15*10^(n-1)+9)=8* reversal(9*10^n+51)=8*reversal(3*p). Also if p=(2*10^n+1)/3 is prime then 123*p is in the sequence (the proof is easy). Next term is greater than 13*10^7.
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EXAMPLE
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82000041 is in the sequence because sigma(82000041)
=112000224=8*14000028=8*reversal(82000041).
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MATHEMATICA
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Do[If[DivisorSigma[1, n]==8*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 130000000}]
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CROSSREFS
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Cf. A069216, A105324, A114928, A115747, A115748.
Sequence in context: A087002 A046394 A108822 this_sequence A105323 A097982 A064321
Adjacent sequences: A115746 A115747 A115748 this_sequence A115750 A115751 A115752
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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), Feb 12 2006
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