A097645 Numbers k such that k = sigma(phi(k) + pi(k)).

1, 6, 54, 78, 1296, 1482, 6480, 6552, 14040, 20160, 36936, 1273896

Offset: 1

Author

Farideh Firoozbakht, Sep 07 2004

Keywords

• nonn
• more
• hard

Comments

Does this sequence have any odd terms > 1? There is no other term up to 3*10^7.

a(13) > 10350781218. - J.W.L. (Jan) Eerland, Dec 25 2021

Examples

			1273896 is in the sequence because pi(1273896) = 98190, phi(1273896) = 391680, and sigma(98190+391680) = 1273896.
		

Crossrefs

Cf. A018784, A082515, A097646.

Programs

Mathematica

Do[If[n==DivisorSigma[1, EulerPhi[n]+PrimePi[n]], Print[n]], {n, 10000000}]
n=1;Monitor[Parallelize[While[True,If[DivisorSigma[1,EulerPhi[n]+PrimePi[n]]==n,Print[n]];n++];n],n] (* J.W.L. (Jan) Eerland, Dec 25 2021 *)

PARI

isok(k) = k == sigma(eulerphi(k) + primepi(k)); \\ Michel Marcus, Dec 25 2021