OFFSET
0,2
MATHEMATICA
AlmostPrimePi[k_Integer, n_] := Module[{a, i}, a[0] = 1; If[k == 1, PrimePi[n], Sum[PrimePi[n/Times @@ Prime[ Array[a, k - 1]]] - a[k - 1] + 1, Evaluate[ Sequence @@ Table[{a[i], a[i - 1], PrimePi[(n/Times @@ Prime[Array[a, i - 1]])^(1/(k - i + 1))]}, {i, k - 1}]] ]]]; (* Eric W. Weisstein, Feb 07 2006 *)
Join[{1}, Table[AlmostPrimePi[n, 6^n], {n, 21}]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Feb 10 2006
EXTENSIONS
a(22)-a(23) from Donovan Johnson, Oct 01 2010
STATUS
approved