OFFSET
1,4
LINKS
Robert G. Wilson v, Table of n, a(n) for n = 1..53
Eric Weisstein's World of Mathematics, Semiprime.
FORMULA
a(n) = A072114(2^n). - R. J. Mathar, Aug 26 2011
MATHEMATICA
ThreeAlmostPrimePi[n_] := Sum[PrimePi[n/(Prime@i*Prime@j)] - j + 1, {i, PrimePi[n^(1/3)]}, {j, i, PrimePi[Sqrt[n/Prime@i]]}]; Table[ ThreeAlmostPrimePi[2^n], {n, 30}]
CROSSREFS
KEYWORD
nonn,less
AUTHOR
Robert G. Wilson v, Dec 29 2006
STATUS
approved