A136542 Numbers n such that sigma(n)=reversal(n)+5.

57, 58, 597, 1642, 5997, 5998, 51718, 160042, 556438, 599997, 5999998, 15810772, 59999997, 59999998, 160000000042

Offset: 1

Author

Farideh Firoozbakht, Jan 08 2008

Keywords

• base
• more
• nonn

Comments

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).

a(16) > 10^12. - Giovanni Resta, Oct 28 2012

Examples

			sigma(57)=80=75+5=reversal(57)+5, so 57 is in the sequence.
		

Crossrefs

Cf. A069216.

Programs

Mathematica

Do[If[DivisorSigma[1,n]==FromDigits@Reverse@IntegerDigits#n+5, Print[n]],{n,160000000}]

Extensions

a(15) from Giovanni Resta, Oct 28 2012