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A120047 Number of 6-almost primes less than or equal to 10^n. 11
0, 0, 2, 37, 485, 5933, 68963, 774078, 8493366, 91683887, 977694273, 10327249593, 108264085934, 1128049914377, 11694704489580 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..14.

EXAMPLE

There are 2 six-almost primes up to 100: 64 & 96.

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[6, 10^n], {n, 0, 13}]

CROSSREFS

Cf. A066265, A014613, A116382.

Cf. A006880, A036352, A109251, A114106, A114453, A120047, A120048, A120049, A120050, A120051, A120052, A120053, A116430.

Sequence in context: A300542 A100849 A300969 * A300926 A216539 A139122

Adjacent sequences:  A120044 A120045 A120046 * A120048 A120049 A120050

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Feb 07 2006

EXTENSIONS

a(14) from Robert G. Wilson v, Jan 07 2007

STATUS

approved

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Last modified September 30 02:48 EDT 2020. Contains 337432 sequences. (Running on oeis4.)