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%I #6 Sep 30 2023 18:48:23
%S 34,394,3994,39994,2309882,3070463,7796129,205207782,225073882,
%T 478854106,644154038,1556396391,3154222593,3165974493,5951924107,
%U 10444787521,12114130241,20611191282,58403366517,71103822309
%N Numbers n such that sigma(n) = 6*(reversal(n)-n).
%C If n=4*10^m-6 is a semiprime (and 2*10^m-3 is prime) then n is in the sequence (the proof is easy). Next term is greater than 7*10^7.
%e sigma(34)=54=6*(43-34)=6*(reversal(34)-34), so 34 is in the sequence.
%t Do[If[6(FromDigits@Reverse@IntegerDigits@n-n)==DivisorSigma[1,n], Print[n]],{n,70000000}]
%Y Cf. A000203, A004086, A135242.
%K base,nonn
%O 1,1
%A _Farideh Firoozbakht_, Jan 04 2008
%E a(8)-a(20) from _Donovan Johnson_, Dec 21 2008
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