

A115749


Numbers n such that sigma(n)=8*reversal(n).


0




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^(n1)+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



