A115749 Numbers n such that sigma(n)=8*reversal(n).

861, 951, 2070, 8241, 900051, 8864151, 9000051, 82000041, 8200000041, 82000000041

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