

A136544


Numbers n such that phi(n)+sigma(n)=reversal(n)+3.


4




OFFSET

1,1


COMMENTS

Next term of the sequence is greater than 10^9. All semiprimes of the form 4*10^m3 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^m3 is semiprime. Is it true that 3 is the only prime term in the sequence?


LINKS



EXAMPLE

phi(168632373)+sigma(168632373)=87744384+285492480=373236861+3= reversal(168632373)+3, so 168632373 is in the sequence.


MATHEMATICA

Do[If[DivisorSigma[1, n]+EulerPhi@n==FromDigits@Reverse@IntegerDigits@n+ 3, Print[n]], {n, 500000000}]


CROSSREFS



KEYWORD

base,more,nonn


AUTHOR



EXTENSIONS



STATUS

approved



