OFFSET
0,6
COMMENTS
The partial sum equals the number of Pi_4(2^n) = A334069(n).
EXAMPLE
(2^4, 2^5] there is one semiprime, namely 24. 16 was counted in the previous entry.
MATHEMATICA
FourAlmostPrimePi[n_] := Sum[ PrimePi[n/(Prime@i*Prime@j*Prime@k)] - k + 1, {i, PrimePi[n^(1/4)]}, {j, i, PrimePi[(n/Prime@i)^(1/3)]}, {k, j, PrimePi@Sqrt[n/(Prime@i*Prime@j)]}]; t = Table[ FourAlmostPrimePi[2^n], {n, 0, 37}]; Rest@t - Most@t
CROSSREFS
KEYWORD
nonn
AUTHOR
Jonathan Vos Post and Robert G. Wilson v, Mar 20 2006
STATUS
approved