A107656 Numbers k such that prime(k) = d(k)*phi(k) + 1, where d(k) is number of positive divisors of k.

1, 2, 3, 4, 652245

Offset: 1

Author

Farideh Firoozbakht, Jun 06 2005

Keywords

• nonn
• more

Comments

There is no further term up to 5*10^7.

a(6) > 10^10, if it exists. - Amiram Eldar, Apr 30 2024

Examples

			652245 is in the sequence because prime(652245) = d(652245)*phi(652245) + 1.
		

Crossrefs

Cf. A000005, A000010, A104905, A107657.

Programs

Mathematica

Do[If[Prime[n] == DivisorSigma[0, n]*EulerPhi[n] + 1, Print[n]], {n, 50000000}]

PARI

lista(pmax) = {my(k = 0, f); forprime(p=1, 1e16, k++; f = factor(k); if(p == numdiv(f)*eulerphi(f)+1, print1(k,", ")));} \\ Amiram Eldar, Apr 30 2024