

A136543


Numbers n such that phi(n)+sigma(n)=4*reversal(n).


2




OFFSET

1,1


COMMENTS

All semiprimes of the form 8*10^m7 are in the sequence  the proof is easy. Next term is greater than 10^8.
a(7) > 10^12.  Giovanni Resta, Nov 03 2012
A100412(n) is in the sequence for n = 2, 4, 7, 9, 11, 16, 18, 23, 31, 32, 40,...  M. F. Hasler, Nov 03 2012


LINKS

Table of n, a(n) for n=1..6.


EXAMPLE

phi(2152311)+sigma(2152311)=1217664+3312384=4*1132512=4*reversal(2152311), so 2152311 is in the sequence.


MATHEMATICA

Do[If[4*FromDigits@Reverse@IntegerDigits@n==EulerPhi@n+ DivisorSigma[1, n], Print[n]], {n, 100000000}]


CROSSREFS

Sequence in context: A133537 A213471 A075667 * A133274 A261657 A086393
Adjacent sequences: A136540 A136541 A136542 * A136544 A136545 A136546


KEYWORD

base,more,nonn


AUTHOR

Farideh Firoozbakht, Jan 20 2008


EXTENSIONS

a(5)a(6) from Giovanni Resta, Nov 03 2012


STATUS

approved



