

A230019


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


4




OFFSET

1,1


COMMENTS

If n=2*10^m7 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.
a(6) > 10^13.  Giovanni Resta, Feb 08 2014


LINKS

Table of n, a(n) for n=1..5.


MATHEMATICA

r[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Do[If[DivisorSigma[1, n] + EulerPhi[n] == r[n]3, Print[n]], {n, 1000000000}]


CROSSREFS

Cf. A000010, A000203, A004086, A070272, A230004, A230005, A230006, A136544, A237521, A237522.
Sequence in context: A094799 A163500 A164321 * A106777 A094800 A200863
Adjacent sequences: A230016 A230017 A230018 * A230020 A230021 A230022


KEYWORD

nonn,base,more


AUTHOR

Farideh Firoozbakht, Dec 02 2013


EXTENSIONS

a(4)a(5) from Giovanni Resta, Feb 06 2014


STATUS

approved



