OFFSET
1,1
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..1000
EXAMPLE
sigma(528) = sigma(825) = 1488.
MATHEMATICA
nd[x_, y_] := 10*x+y tn[x_] := Fold[nd, 0, x] red[x_] := Reverse[IntegerDigits[x]] Do[s=DivisorSigma[1, n]; s1=DivisorSigma[1, tn[red[n]]]; If[Equal[s, s1]&&!Equal[n, tn[red[n]]], Print[{n, s}]], {n, 1, 1000000}]
srnQ[n_]:=Module[{idn=IntegerDigits[n], ridn}, ridn=Reverse[idn]; idn!=ridn && DivisorSigma[1, n]==DivisorSigma[1, FromDigits[ridn]]]; Select[Range[ 100000], srnQ] (* Harvey P. Dale, Oct 25 2011 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Jul 04 2003
STATUS
approved