A104904 Numbers n such that d(n)*pi(n)=n, where d(n) is the number of positive divisors of n.

2, 8408, 481044, 189961452, 75370122528, 75370124832, 4086199302976, 221945984411264

Offset: 1

Author

Farideh Firoozbakht, Apr 12 2005

Keywords

• hard
• more
• nonn

Comments

Next term is greater than 3*10^9.

Examples

			189961452 is in the sequence because d(189961452)=18; pi(189961452)=10553414 & 18*10553414=189961452.
		

Crossrefs

Cf. A063903, A104905, A104906.

Programs

Mathematica

Do[If[DivisorSigma[0, n]*PrimePi[n] == n, Print[n]], {n, 2000000000}]

Extensions

a(5)-a(8) from Donovan Johnson, Dec 08 2009