|
|
A104904
|
|
Numbers n such that d(n)*pi(n)=n, where d(n) is the number of positive divisors of n.
|
|
2
|
|
|
|
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
|
|
|
|