A230015 Numbers n such that reversal(n) = sigma(n)+2n.

2475247, 26522529

Offset

1,1

Comments

If p(m) = (1/101)*(25*10^(4m-1)-53) is prime then p(m) is a term of the sequence. a(1) = p(1) and p(2669) is the second term of this form, which is a 10675-digit prime. This implies a(3) exists and a(3) <= 10^10675. a(3) is greater than 10^9.

a(3) > 10^13. - Giovanni Resta, Feb 08 2014

Links

Table of n, a(n) for n=1..2.

Mathematica

Do[If[FromDigits[Reverse[IntegerDigits[n]]]==DivisorSigma[1, n]+2n, Print[n]], {n, 27000000}]

Crossrefs

Cf. A000010, A000203, A004086.

Sequence in context: A254774 A254781 A254727 * A180705 A286036 A215814

Adjacent sequences: A230012 A230013 A230014 * A230016 A230017 A230018

Keyword

nonn,base,bref,more

Author

Farideh Firoozbakht, Nov 15 2013

Status

approved