A178326 Numbers n such that n is the mean value of phi(n) and reversal(n).

1, 2994, 25524, 29994, 47817, 48618, 299994, 29999994, 48108108108

Offset

1,2

Comments

If p=5*10^m-1 is prime then n=6*p is in the sequence (the proof is easy).

a(10) > 2*10^11. - Donovan Johnson, Nov 10 2011

a(10) > 10^12. - Giovanni Resta, Oct 28 2012

If p=1/111*(10^(3m+3)-1)-5*10^(3m) is prime then n=12*p is in the sequence. For m = 3,47,75,203,1259 ... p is prime. - Farideh Firoozbakht, Oct 04 2013

Links

Table of n, a(n) for n=1..9.

Example

(1/2)*(phi(25524)+reversal(25524)) = (1/2)*(8496+42552) = 25524, so 25524 is in the sequence.

Mathematica

r[n_]:=FromDigits[Reverse[IntegerDigits[n]]];
Do[If[EulerPhi[n]+r[n]==2n, Print[n]], {n, 320000000}]

Crossrefs

Cf. A000010, A004086.

Sequence in context: A253758 A230013 A158963 * A063055 A235754 A235529

Adjacent sequences: A178323 A178324 A178325 * A178327 A178328 A178329

Keyword

base,more,nonn

Author

Farideh Firoozbakht, May 29 2010

Extensions

a(9) from Donovan Johnson, Nov 10 2011

Status

approved