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%I #10 Sep 30 2023 18:47:56
%S 10,51,430,591,922,5991,8350,20210,28810,59211,59991,6673581,8179030,
%T 20158910,203887910,833549650,2263048910,2814442310,7823347543,
%U 78551146723,81896108650,281444442310,770920338133,832428872110,7670112536751
%N Numbers n such that sigma(n) = 2*(n-reversal(n)).
%C If n=6*10^m-9 is semiprime then n is in the sequence (the proof is easy).
%C a(26) > 10^13. - _Giovanni Resta_, Jul 13 2015
%e sigma(51)=72=2*(51-15)=2*(51-reversal(51)), so 51 is in the sequence.
%t Do[If[2(n-FromDigits@Reverse@IntegerDigits@n)==DivisorSigma[1,n], Print[n]],{n,70000000}]
%Y Cf. A000203, A004086, A135243.
%K base,more,nonn
%O 1,1
%A _Farideh Firoozbakht_, Jan 04 2008
%E a(15)-a(21) from _Donovan Johnson_, Dec 21 2008
%E a(22)-a(25) from _Giovanni Resta_, Jul 13 2015