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A104904 Numbers n such that d(n)*pi(n)=n, where d(n) is the number of positive divisors of n. 2
2, 8408, 481044, 189961452, 75370122528, 75370124832, 4086199302976, 221945984411264 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Next term is greater than 3*10^9.

LINKS

Table of n, a(n) for n=1..8.

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

Cf. A063903, A104905, A104906.

Sequence in context: A322126 A272241 A171939 * A272247 A167748 A203755

Adjacent sequences: A104901 A104902 A104903 * A104905 A104906 A104907

KEYWORD

hard,more,nonn

AUTHOR

Farideh Firoozbakht, Apr 12 2005

EXTENSIONS

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

STATUS

approved

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Last modified March 24 22:08 EDT 2023. Contains 361511 sequences. (Running on oeis4.)