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A120049 Number of 8-almost primes less than or equal to 10^n. 12
0, 0, 0, 7, 105, 1418, 17572, 207207, 2367507, 26483012, 291646797, 3173159326, 34192782745, 365561221293, 3882841742380 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,4
LINKS
EXAMPLE
There are 7 eight-almost primes up to 1000: 256, 384, 576, 640, 864, 896 & 960.
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 *)
Table[AlmostPrimePi[8, 10^n], {n, 12}]
CROSSREFS
Sequence in context: A098362 A093741 A139742 * A067420 A368351 A358957
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Feb 07 2006
EXTENSIONS
a(13) and a(14) from Robert G. Wilson v, Jan 07 2007
Example corrected by Harvey P. Dale, Aug 13 2018
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)