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A116427
The number of n-almost primes less than or equal to 6^n, starting with a(0)=1.
8
1, 3, 13, 50, 200, 726, 2613, 9061, 30779, 102637, 338230, 1102674, 3566001, 11455355, 36597558, 116395587, 368749900, 1164407829, 3666312894, 11515047829, 36085395700, 112857846859, 352329509934, 1098136237818
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}]]
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Feb 10 2006
EXTENSIONS
a(22)-a(23) from Donovan Johnson, Oct 01 2010
STATUS
approved