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 A115749 Numbers n such that sigma(n)=8*reversal(n). 0
 861, 951, 2070, 8241, 900051, 8864151, 9000051, 82000041, 8200000041, 82000000041 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. a(11) > 10^12. - Giovanni Resta, Oct 28 2012 LINKS Table of n, a(n) for n=1..10. EXAMPLE 82000041 is in the sequence because sigma(82000041) =112000224=8*14000028=8*reversal(82000041). MATHEMATICA Do[If[DivisorSigma[1, n]==8*FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 130000000}] CROSSREFS Cf. A069216, A105324, A114928, A115747, A115748. Sequence in context: A278156 A249461 A292626 * A105323 A206756 A203272 Adjacent sequences: A115746 A115747 A115748 * A115750 A115751 A115752 KEYWORD base,more,nonn AUTHOR Farideh Firoozbakht, Feb 12 2006 EXTENSIONS a(9)-a(10) from Donovan Johnson, Dec 21 2008 STATUS approved

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Last modified July 14 05:06 EDT 2024. Contains 374291 sequences. (Running on oeis4.)