%I #20 Feb 09 2014 04:15:21
%S 199993,17333334,19999993,199999999993,1999999999993
%N Numbers n such that sigma(n) + phi(n) = reversal(n) - 3.
%C If n=2*10^m-7 is a semiprime then n is in the sequence. Also if p=(1/999)*(962*1000^m+37) is prime then 18*p is in the sequence. All known terms are of these two forms.
%C a(6) > 10^13. - _Giovanni Resta_, Feb 08 2014
%t r[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Do[If[DivisorSigma[1, n] + EulerPhi[n] == r[n]-3, Print[n]], {n, 1000000000}]
%Y Cf. A000010, A000203, A004086, A070272, A230004, A230005, A230006, A136544, A237521, A237522.
%K nonn,base,more
%O 1,1
%A _Farideh Firoozbakht_, Dec 02 2013
%E a(4)-a(5) from _Giovanni Resta_, Feb 06 2014