A104906 Numbers n such that d(n)*reversal(n)=phi(n), where d(n) is number of positive divisors of n.

1, 10, 831, 8310

Offset: 1

Author

Farideh Firoozbakht, Apr 14 2005

Keywords

• more
• nonn

Comments

If n is a term of this sequence and gcd(10,n)=1 then 10*n is also in the sequence because reversal(10*n)=reversal(n); d(10)=phi(10) and both functions d & phi are multiplicative. No further terms up to 350000000.

a(5) > 10^12. - Giovanni Resta, Apr 25 2017

Examples

			8310 is in the sequence because d(8310)=16; reversal(8310)=138;
phi(8310)=2208 & 16*138=2108.
		

Crossrefs

Cf. A063903, A104904, A104905, A104907.

Programs

Mathematica

reversal[n_]:= FromDigits[Reverse[IntegerDigits[n]]]; Do[If[DivisorSigma[0, n]*reversal[n] == EulerPhi[n], Print[n]], {n, 350000000}]