The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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