OFFSET
1,18
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
a(n) ~ c * n, where c = (6/Pi^2) * Sum_{p prime} 1/(p*(p+1)) = 0.200755... (A271971). - Amiram Eldar, Feb 16 2021
MATHEMATICA
cfnsQ[n_]:=Module[{f=FactorInteger[n][[All, 2]]}, Max[f]<3&&Count[f, 2] == 1&&!IntegerQ[Sqrt[n]]]; Accumulate[Table[If[cfnsQ[n], 1, 0], {n, 100}]] (* Harvey P. Dale, May 24 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jul 19 2002
STATUS
approved