Search: id:A136544
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%I A136544
%S A136544 3,3997,3999997,168632373
%N A136544 Numbers n such that phi(n)+sigma(n)=reversal(n)+3.
%C A136544 Next term of the sequence is greater than 10^9. All semiprimes of the 
               form 4*10^m-3 are in the sequence - the proof is easy. For m=3,6,
               11,12,13,15,16,18,19,24,38,56,60,... 4*10^m-3 is semiprime. Is it 
               true that, 3 is the only prime term in the sequence?
%e A136544 phi(168632373)+sigma(168632373)=87744384+285492480=373236861+3= reversal(168632373)+3, 
               so 168632373 is in the sequence.
%t A136544 Do[If[DivisorSigma[1,n]+EulerPhi@n==FromDigits@Reverse@IntegerDigits@n+ 
               3,Print[n]],{n,500000000}]
%Y A136544 Cf. A136545, A136546.
%Y A136544 Sequence in context: A003831 A089895 A116213 this_sequence A024048 A094319 
               A003166
%Y A136544 Adjacent sequences: A136541 A136542 A136543 this_sequence A136545 A136546 
               A136547
%K A136544 base,more,nonn
%O A136544 1,1
%A A136544 Farideh Firoozbakht (mymontain(AT)yahoo.com), Jan 20 2008

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