A069216 - OEIS

%I #13 Aug 29 2017 14:57:06

%S 1,69,276,639,2556

%N Numbers n such that sigma(n) = reversal(n).

%C There is no further term up to 10^10. - _Farideh Firoozbakht_, Jan 20 2008

%C There is no further term up to 10^13. - _Giovanni Resta_, Jul 13 2015

%e sigma(2556) = 6552 = reversal(2556), so 2556 belongs to the sequence.

%t Do[If[DivisorSigma[1, n] == FromDigits[Reverse[IntegerDigits[n]]], Print[n]], {n, 1, 10^5}]

%t Select[Range[3000],DivisorSigma[1,#]==IntegerReverse[#]&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 29 2017 *)

%K base,nonn

%O 1,2

%A _Joseph L. Pe_, Apr 11 2002