OFFSET
1,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
MATHEMATICA
SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; nn = 100; t = Select[Range[nn^2], SemiPrimeQ]; Table[Length[Select[t, # <= n^2 &]], {n, nn}] (* T. D. Noe, Jan 30 2012 *)
Module[{nn=60, sp}, sp=Accumulate[Table[If[PrimeOmega[n]==2, 1, 0], {n, nn^2}]]; Table[sp[[i^2]], {i, nn}]] (* Harvey P. Dale, May 29 2014 *)
PROG
(Python)
from sympy import prime, primepi
def A205726(n): return int(sum(primepi(n**2//prime(k))-k+1 for k in range(1, primepi(n)+1))) # Chai Wah Wu, Jul 23 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Keith Backman, Jan 30 2012
STATUS
approved