OFFSET
1,1
COMMENTS
FORMULA
Sum_{n>=1} 1/a(n) = (P(3)^2 - P(6))/2 = (A085541^2 - A085966)/2 = 0.006735..., where P is the prime zeta function. - Amiram Eldar, Jul 06 2020
EXAMPLE
216=2^3*3^3. 1000=2^3*5^3. 2744=2^3*7^3.
MATHEMATICA
fQ[n_]:=Last/@FactorInteger[n]=={3, 3}; lst={}; Do[If[fQ[n], AppendTo[lst, n]], {n, 6*9!}]; lst
With[{nn=30}, Select[Union[(Times@@@Subsets[Prime[Range[nn]], {2}])^3], #<= (2Prime[ nn])^3&]](* Harvey P. Dale, May 27 2024 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Joseph Stephan Orlovsky, Jun 25 2009
EXTENSIONS
Definition rephrased by R. J. Mathar, Jun 27 2009
STATUS
approved